diff --git a/postfix/HISTORY b/postfix/HISTORY index e1ecaf221..4041f3dc6 100644 --- a/postfix/HISTORY +++ b/postfix/HISTORY @@ -27213,16 +27213,36 @@ Apologies for any names omitted. a configured recipient delimiter value. Reported by Tod A. Sandman. Files: proto/postconf.proto, local/local_expand.c. -20231221 +20240109 - Security: with "smtpd_forbid_bare_newline = yes" (default - "no" for Postfix < 3.9), reply with "Error: bare - received" and disconnect when an SMTP client sends a line - ending in , violating the RFC 5321 requirement that - lines must end in . This prevents SMTP smuggling - attacks that target a recipient at a Postfix server. For - backwards compatibility, local clients are excluded by + Security (outbound SMTP smuggling): with the default setting + "cleanup_replace_stray_cr_lf = yes" Postfix will replace + stray or characters in message content with a + space character. This prevents Postfix from enabling + outbound (remote) SMTP smuggling, and it also makes evaluation + of Postfix-added DKIM etc. signatures independent from how + a remote mail server handles stray or characters. + Files: global/mail_params.h, cleanup/cleanup.c, + cleanup/cleanup_message.c, mantools/postlink, proto/postconf.proto. + +20240112 + + Security (inbound SMTP smuggling): with "smtpd_forbid_bare_newline + = normalize" (default "no" for Postfix < 3.9), the Postfix + SMTP server requires the standard End-of-DATA sequence + ., and otherwise allows command or message + content lines ending in the non-standard , processing + them as if the client sent the standard . + + The alternative setting, "smtpd_forbid_bare_newline = reject" + will reject any command or message that contains a bare + , and is more likely to cause problems with legitimate + clients. + + For backwards compatibility, local clients are excluded by default with "smtpd_forbid_bare_newline_exclusions = - $mynetworks". Files: mantools/postlink, proto/postconf.proto, + $mynetworks". + + Files: mantools/postlink, proto/postconf.proto, global/mail_params.h, global/smtp_stream.c, global/smtp_stream.h, - smtpd/smtpd.c. + smtpd/smtpd.c, smtpd/smtpd_check.[hc]. diff --git a/postfix/RELEASE_NOTES b/postfix/RELEASE_NOTES index d7a112ea4..0a23bf80c 100644 --- a/postfix/RELEASE_NOTES +++ b/postfix/RELEASE_NOTES @@ -25,31 +25,104 @@ now also distributed with the more recent Eclipse Public License (EPL) 2.0. Recipients can choose to take the software under the license of their choice. Those who are more comfortable with the IPL can continue with that license. - -Major changes with Postfix 3.8.4 -================================ -Security: the Postfix SMTP server optionally disconnects a remote -SMTP client that sends a 'bare newline' line ending in SMTP. This -prevents an SMTP smuggling attack on recipients at a Postfix server. -For background, see https://www.postfix.org/smtp-smuggling.html +Incompatibility with Postfix 3.8.5, 3.7.10, 3.6.14, and 3.5.24 +============================================================== -Sites concerned about SMTP smuggling attacks should enable this -feature in Internet-facing Postfix servers. For compatibility with -non-standard clients, Postfix by default excludes clients in -mynetworks from this countermeasure. +Improvements for outbound SMTP smuggling defense: -The default settings are: +- With "cleanup_replace_stray_cr_lf = yes" (the default), the cleanup + daemon replaces each stray or character in message + content with a space character. The replacement happens before + any other content management (header/body_checks, Milters, etc). - # Optionally disconnect remote SMTP clients that send bare newlines, - # but allow local clients with non-standard SMTP implementations - # such as netcat, fax machines, or load balancer health checks. + This prevents outbound SMTP smuggling, where an attacker uses + Postfix to send email containing a non-standard End-of-DATA + sequence, to exploit inbound SMTP smuggling at a vulnerable remote + SMTP server. + + This also improves the remote evaluation of Postfix-added DKIM + and other signatures, as the evaluation result will not depend + on how a remote email server handles stray or characters. + +This feature applies to all email that Postfix locally or remotely +sends out. It is not allowlisted based on client identity. + +Major changes with Postfix 3.8.5, 3.7.10, 3.6.14, and 3.5.24 +============================================================ + +Improvements for inbound SMTP smuggling defense: + +- Better compatibility: the recommended setting "smtpd_forbid_bare_newline + = normalize" requires the standard End-of-DATA sequence + ., but allows bare newlines from SMTP clients, + maintaining more compatibility with existing infrastructure. + +- Improved logging for rejected input (it now includes queue ID, + helo, mail, and rcpt, if available). + +- The setting "smtpd_forbid_bare_newline = reject" requires + that input lines end in , requires the standard End-of-DATA + sequence ., and rejects a command or message that + contains a bare newline. To disconnect the client, specify + "smtpd_forbid_bare_newline_reject_code = 521". + +- The Postfix SMTP server no longer strips extra as in + ., to silence false alarms from test tools + that send attack sequences that real mail servers cannot send. + Details at https://www.postfix.org/false-smuggling-claims.html + +- The old setting "yes" has become an alias for "normalize". + +- The old setting "no" has not changed, and allows SMTP smuggling. + +The recommended settings are now: + + # Require the standard End-of-DATA sequence .. + # Otherwise, allow bare and process it as if the client sent + # . # - smtpd_forbid_bare_newline = no + # This maintains compatibility with many legitimate SMTP client + # applications that send a mix of standard and non-standard line + # endings, but will fail to receive email from client implementations + # that do not terminate DATA content with the standard End-of-DATA + # sequence .. + # + # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. + # The example below allowlists SMTP clients in trusted networks. + # + smtpd_forbid_bare_newline = normalize smtpd_forbid_bare_newline_exclusions = $mynetworks -This feature is back-ported from Postfix 3.9, with the difference -that "smtpd_forbid_bare_newline = no" by default. +Alternative settings: + + # Reject input lines that contain and log a "bare received" + # error. Require that input lines end in , and require the + # standard End-of-DATA sequence .. + # + # This will reject email from SMTP clients that send any non-standard + # line endings such as web applications, netcat, or load balancer + # health checks. + # + # This will also reject email from services that use BDAT to send + # MIME text containing a bare newline (RFC 3030 Section 3 requires + # canonical MIME format for text message types, defined in RFC 2045 + # Sections 2.7 and 2.8). + # + # Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. + # The example below allowlists SMTP clients in trusted networks. + # + smtpd_forbid_bare_newline = reject + smtpd_forbid_bare_newline_exclusions = $mynetworks + # + # Alternatively, in the case of BDAT violations, BDAT can be selectively + # disabled with smtpd_discard_ehlo_keyword_address_maps, or globally + # disabled with smtpd_discard_ehlo_keywords. + # + # smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file + # /path/to/file: + # 10.0.0.0/24 chunking, silent-discard + # smtpd_discard_ehlo_keywords = chunking, silent-discard Major changes with Postfix 3.8.1 ================================ diff --git a/postfix/html/cleanup.8.html b/postfix/html/cleanup.8.html index 811b93031..6e662f6d3 100644 --- a/postfix/html/cleanup.8.html +++ b/postfix/html/cleanup.8.html @@ -160,6 +160,16 @@ CLEANUP(8) CLEANUP(8) The set of characters that Postfix will remove from message con- tent. + Available in Postfix version 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24, and + later: + + cleanup_replace_stray_cr_lf (yes) + Replace each stray <CR> or <LF> character in message content + with a space character, to prevent outbound SMTP smuggling, and + to make the evaluation of Postfix-added DKIM or other signatures + independent from how a remote mail server handles such charac- + ters. + BEFORE QUEUE MILTER CONTROLS As of version 2.3, Postfix supports the Sendmail version 8 Milter (mail filter) protocol. When mail is not received via the smtpd(8) server, diff --git a/postfix/html/postconf.5.html b/postfix/html/postconf.5.html index 50d71748d..dbb8cc823 100644 --- a/postfix/html/postconf.5.html +++ b/postfix/html/postconf.5.html @@ -1463,6 +1463,40 @@ Examples: + + +
cleanup_replace_stray_cr_lf +(default: yes)
+ +

Replace each stray <CR> or <LF> character in message +content with a space character, to prevent outbound SMTP smuggling, +and to make the evaluation of Postfix-added DKIM or other signatures +independent from how a remote mail server handles such characters. +

+ +

SMTP does not allow such characters unless they are part of a +<CR><LF> sequence, and different mail systems handle +such stray characters in an implementation-dependent manner. Stray +<CR> or <LF> characters could be used for outbound +SMTP smuggling, where an attacker uses a Postfix server to send +message content with a non-standard End-of-DATA sequence that +triggers inbound SMTP smuggling at a remote SMTP server.

+ +

The replacement happens before all other content management, +and before Postfix may add a DKIM etc. signature; if the signature +were created first, the replacement could invalidate the signature. +

+ +

In addition to preventing SMTP smuggling, replacing stray +<CR> or <LF> characters ensures that the result of +signature validation by later mail system will not depend on how +that mail system handles those stray characters in an +implementation-dependent manner.

+ +

This feature is available in Postfix ≥ 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24.

+ +
cleanup_service_name @@ -15609,32 +15643,118 @@ This feature is available in Postfix 2.0 and later.
smtpd_forbid_bare_newline (default: Postfix < 3.9: no)
-

Reply with "Error: bare <LF> received" and disconnect -when a remote SMTP client sends a line ending in <LF>, violating -the RFC 5321 requirement that lines must end in <CR><LF>. -This feature is disbled by default with Postfix < 3.9. Use -smtpd_forbid_bare_newline_exclusions to exclude non-standard clients -such as netcat. Specify "smtpd_forbid_bare_newline = no" to disable -(not recommended for an Internet-connected MTA).

+

Reject or restrict input lines from an SMTP client that end in +<LF> instead of the standard <CR><LF>. Such line +endings are commonly allowed with UNIX-based SMTP servers, but they +violate RFC 5321, and allowing such line endings can make a server +vulnerable to +SMTP smuggling.

-

See -https://www.postfix.org/smtp-smuggling.html for details. +

Specify one of the following values (case does not matter):

-

Example:

+
+ +
normalize
Require the standard +End-of-DATA sequence <CR><LF>.<CR><LF>. +Otherwise, allow command or message content lines ending in the +non-standard <LF>, and process them as if the client sent the +standard <CR><LF>.

This maintains compatibility +with many legitimate SMTP client applications that send a mix of +standard and non-standard line endings, but will fail to receive +email from client implementations that do not terminate DATA content +with the standard End-of-DATA sequence +<CR><LF>.<CR><LF>.

Such clients +can be excluded with smtpd_forbid_bare_newline_exclusions.
+ +
yes
Compatibility alias for normalize.
+ +
reject
Require the standard End-of-DATA +sequence <CR><LF>.<CR><LF>. Reject a command +or message content when a line contains bare <LF>, log a "bare +<LF> received" error, and reply with the SMTP status code in +$smtpd_forbid_bare_newline_reject_code.

This will reject +email from SMTP clients that send any non-standard line endings +such as web applications, netcat, or load balancer health checks. +

This will also reject email from services that use BDAT +to send MIME text containing a bare newline (RFC 3030 Section 3 +requires canonical MIME format for text message types, defined in +RFC 2045 Sections 2.7 and 2.8).

Such clients can be +excluded with smtpd_forbid_bare_newline_exclusions (or, in the case +of BDAT violations, BDAT can be selectively disabled with +smtpd_discard_ehlo_keyword_address_maps, or globally disabled with +smtpd_discard_ehlo_keywords).
+ +
no (default)
Do not require the standard +End-of-DATA +sequence <CR><LF>.<CR><LF>. Always process +a bare <LF> as if the client sent <CR><LF>. This +option is fully backwards compatible, but is not recommended for +an Internet-facing SMTP server, because it is vulnerable to SMTP smuggling. +
+ +
+ +

Recommended settings: 

-# Disconnect remote SMTP clients that send bare newlines, but allow
-# local clients with non-standard SMTP implementations such as netcat,
-# fax machines, or load balancer health checks.
+# Require the standard End-of-DATA sequence <CR><LF>.<CR><LF>.
+# Otherwise, allow bare <LF> and process it as if the client sent
+# <CR><LF>.
 #
-smtpd_forbid_bare_newline = yes
+# This maintains compatibility with many legitimate SMTP client
+# applications that send a mix of standard and non-standard line
+# endings, but will fail to receive email from client implementations
+# that do not terminate DATA content with the standard End-of-DATA
+# sequence <CR><LF>.<CR><LF>.
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = normalize
 smtpd_forbid_bare_newline_exclusions = $mynetworks
-

This feature is available in Postfix ≥ 3.9, 3.8.4, 3.7.9, -3.6.13, and 3.5.23.

+

Alternative:

+ +
+
+# Reject input lines that contain <LF> and log a "bare <LF> received"
+# error. Require that input lines end in <CR><LF>, and require the
+# standard End-of-DATA sequence <CR><LF>.<CR><LF>.
+#
+# This will reject email from SMTP clients that send any non-standard
+# line endings such as web applications, netcat, or load balancer
+# health checks.
+#
+# This will also reject email from services that use BDAT to send
+# MIME text containing a bare newline (RFC 3030 Section 3 requires
+# canonical MIME format for text message types, defined in RFC 2045
+# Sections 2.7 and 2.8).
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = reject
+smtpd_forbid_bare_newline_exclusions = $mynetworks
+#
+# Alternatively, in the case of BDAT violations, BDAT can be selectively
+# disabled with smtpd_discard_ehlo_keyword_address_maps, or globally
+# disabled with smtpd_discard_ehlo_keywords.
+#
+# smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file
+# /path/to/file:
+#     10.0.0.0/24 chunking, silent-discard
+# smtpd_discard_ehlo_keywords = chunking, silent-discard
+
+
+ +

This feature with settings yes and no is available +in Postfix 3.8.4, 3.7.9, 3.6.13, and 3.5.23. Additionally, the +settings reject, and normalize are available with +Postfix ≥ 3.9, 3.8.5, 3.7.10, 3.6.14, and 3.5.24.

@@ -15643,26 +15763,28 @@ https://www.postfix.org/smtp-smuggling.html for details. (default: $mynetworks)

Exclude the specified clients from smtpd_forbid_bare_newline -enforcement. It uses the same syntax and parent-domain matching -behavior as mynetworks.

- -

Example:

- -
-
-# Disconnect remote SMTP clients that send bare newlines, but allow
-# local clients with non-standard SMTP implementations such as netcat,
-# fax machines, or load balancer health checks.
-#
-smtpd_forbid_bare_newline = yes
-smtpd_forbid_bare_newline_exclusions = $mynetworks
-
-
+enforcement. This setting uses the same syntax and parent-domain +matching behavior as mynetworks.

This feature is available in Postfix ≥ 3.9, 3.8.4, 3.7.9, 3.6.13, and 3.5.23.

+
+ +
smtpd_forbid_bare_newline_reject_code +(default: 550)
+ +

+The numerical Postfix SMTP server response code when rejecting a +request with "smtpd_forbid_bare_newline = reject". +Specify a 5XX status code (521 to disconnect). +

+ +

This feature is available in Postfix ≥ 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24.

+ +
smtpd_forbid_unauth_pipelining diff --git a/postfix/html/smtpd.8.html b/postfix/html/smtpd.8.html index 27adc66dc..672302a83 100644 --- a/postfix/html/smtpd.8.html +++ b/postfix/html/smtpd.8.html @@ -990,14 +990,19 @@ SMTPD(8) SMTPD(8) Available in Postfix 3.9, 3.8.4, 3.7.9, 3.6.13, 3.5.23 and later: smtpd_forbid_bare_newline (Postfix < 3.9: no) - Reply with "Error: bare <LF> received" and disconnect when a - remote SMTP client sends a line ending in <LF>, violating the - RFC 5321 requirement that lines must end in <CR><LF>. + Reject or restrict input lines from an SMTP client that end in + <LF> instead of the standard <CR><LF>. smtpd_forbid_bare_newline_exclusions ($mynetworks) - Exclude the specified clients from smtpd_forbid_bare_newline + Exclude the specified clients from smtpd_forbid_bare_newline enforcement. + Available in Postfix 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24 and later: + + smtpd_forbid_bare_newline_reject_code (550) + The numerical Postfix SMTP server response code when rejecting a + request with "smtpd_forbid_bare_newline = reject". + TARPIT CONTROLS When a remote SMTP client makes errors, the Postfix SMTP server can insert delays before responding. This can help to slow down run-away diff --git a/postfix/man/man5/postconf.5 b/postfix/man/man5/postconf.5 index 0bc3f3ab5..196a700ef 100644 --- a/postfix/man/man5/postconf.5 +++ b/postfix/man/man5/postconf.5 @@ -878,6 +878,32 @@ canonical_maps = hash:/etc/postfix/canonical .fi .ad .ft R +.SH cleanup_replace_stray_cr_lf (default: yes) +Replace each stray or character in message +content with a space character, to prevent outbound SMTP smuggling, +and to make the evaluation of Postfix\-added DKIM or other signatures +independent from how a remote mail server handles such characters. +.PP +SMTP does not allow such characters unless they are part of a + sequence, and different mail systems handle +such stray characters in an implementation\-dependent manner. Stray + or characters could be used for outbound +SMTP smuggling, where an attacker uses a Postfix server to send +message content with a non\-standard End\-of\-DATA sequence that +triggers inbound SMTP smuggling at a remote SMTP server. +.PP +The replacement happens before all other content management, +and before Postfix may add a DKIM etc. signature; if the signature +were created first, the replacement could invalidate the signature. +.PP +In addition to preventing SMTP smuggling, replacing stray + or characters ensures that the result of +signature validation by later mail system will not depend on how +that mail system handles those stray characters in an +implementation\-dependent manner. +.PP +This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24. .SH cleanup_service_name (default: cleanup) The name of the \fBcleanup\fR(8) service. This service rewrites addresses into the standard form, and performs \fBcanonical\fR(5) address mapping @@ -10727,60 +10753,153 @@ parameter $name expansion. .PP This feature is available in Postfix 2.0 and later. .SH smtpd_forbid_bare_newline (default: Postfix < 3.9: no) -Reply with "Error: bare received" and disconnect -when a remote SMTP client sends a line ending in , violating -the RFC 5321 requirement that lines must end in . -This feature is disbled by default with Postfix < 3.9. Use -smtpd_forbid_bare_newline_exclusions to exclude non\-standard clients -such as netcat. Specify "smtpd_forbid_bare_newline = no" to disable -(not recommended for an Internet\-connected MTA). +Reject or restrict input lines from an SMTP client that end in + instead of the standard . Such line +endings are commonly allowed with UNIX\-based SMTP servers, but they +violate RFC 5321, and allowing such line endings can make a server +vulnerable to +SMTP smuggling. .PP -See -https://www.postfix.org/smtp\-smuggling.html for details. +Specify one of the following values (case does not matter): +.IP "\fBnormalize\fR" +Require the standard +End\-of\-DATA sequence .. +Otherwise, allow command or message content lines ending in the +non\-standard , and process them as if the client sent the +standard . +.br +.br +This maintains compatibility +with many legitimate SMTP client applications that send a mix of +standard and non\-standard line endings, but will fail to receive +email from client implementations that do not terminate DATA content +with the standard End\-of\-DATA sequence +.. +.br +.br +Such clients +can be excluded with smtpd_forbid_bare_newline_exclusions. +.br +.IP "\fByes\fR" +Compatibility alias for \fBnormalize\fR. +.br +.IP "\fBreject\fR" +Require the standard End\-of\-DATA +sequence .. Reject a command +or message content when a line contains bare , log a "bare + received" error, and reply with the SMTP status code in +$smtpd_forbid_bare_newline_reject_code. +.br +.br +This will reject +email from SMTP clients that send any non\-standard line endings +such as web applications, netcat, or load balancer health checks. +.br +.br +This will also reject email from services that use BDAT +to send MIME text containing a bare newline (RFC 3030 Section 3 +requires canonical MIME format for text message types, defined in +RFC 2045 Sections 2.7 and 2.8). +.br +.br +Such clients can be +excluded with smtpd_forbid_bare_newline_exclusions (or, in the case +of BDAT violations, BDAT can be selectively disabled with +smtpd_discard_ehlo_keyword_address_maps, or globally disabled with +smtpd_discard_ehlo_keywords). +.br +.IP "\fBno\fR (default)" +Do not require the standard +End\-of\-DATA +sequence .. Always process +a bare as if the client sent . This +option is fully backwards compatible, but is not recommended for +an Internet\-facing SMTP server, because it is vulnerable to SMTP smuggling. +.br +.br .PP -Example: +Recommended settings: .sp .in +4 .nf .na .ft C -# Disconnect remote SMTP clients that send bare newlines, but allow -# local clients with non\-standard SMTP implementations such as netcat, -# fax machines, or load balancer health checks. +# Require the standard End\-of\-DATA sequence .. +# Otherwise, allow bare and process it as if the client sent +# . # -smtpd_forbid_bare_newline = yes +# This maintains compatibility with many legitimate SMTP client +# applications that send a mix of standard and non\-standard line +# endings, but will fail to receive email from client implementations +# that do not terminate DATA content with the standard End\-of\-DATA +# sequence .. +# +# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. +# The example below allowlists SMTP clients in trusted networks. +# +smtpd_forbid_bare_newline = normalize smtpd_forbid_bare_newline_exclusions = $mynetworks .fi .ad .ft R .in -4 .PP -This feature is available in Postfix >= 3.9, 3.8.4, 3.7.9, -3.6.13, and 3.5.23. +Alternative: +.sp +.in +4 +.nf +.na +.ft C +# Reject input lines that contain and log a "bare received" +# error. Require that input lines end in , and require the +# standard End\-of\-DATA sequence .. +# +# This will reject email from SMTP clients that send any non\-standard +# line endings such as web applications, netcat, or load balancer +# health checks. +# +# This will also reject email from services that use BDAT to send +# MIME text containing a bare newline (RFC 3030 Section 3 requires +# canonical MIME format for text message types, defined in RFC 2045 +# Sections 2.7 and 2.8). +# +# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions. +# The example below allowlists SMTP clients in trusted networks. +# +smtpd_forbid_bare_newline = reject +smtpd_forbid_bare_newline_exclusions = $mynetworks +# +# Alternatively, in the case of BDAT violations, BDAT can be selectively +# disabled with smtpd_discard_ehlo_keyword_address_maps, or globally +# disabled with smtpd_discard_ehlo_keywords. +# +# smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file +# /path/to/file: +# 10.0.0.0/24 chunking, silent\-discard +# smtpd_discard_ehlo_keywords = chunking, silent\-discard +.fi +.ad +.ft R +.in -4 +.PP +This feature with settings \fByes\fR and \fBno\fR is available +in Postfix 3.8.4, 3.7.9, 3.6.13, and 3.5.23. Additionally, the +settings \fBreject\fR, and \fBnormalize\fR are available with +Postfix >= 3.9, 3.8.5, 3.7.10, 3.6.14, and 3.5.24. .SH smtpd_forbid_bare_newline_exclusions (default: $mynetworks) Exclude the specified clients from smtpd_forbid_bare_newline -enforcement. It uses the same syntax and parent\-domain matching -behavior as mynetworks. -.PP -Example: -.sp -.in +4 -.nf -.na -.ft C -# Disconnect remote SMTP clients that send bare newlines, but allow -# local clients with non\-standard SMTP implementations such as netcat, -# fax machines, or load balancer health checks. -# -smtpd_forbid_bare_newline = yes -smtpd_forbid_bare_newline_exclusions = $mynetworks -.fi -.ad -.ft R -.in -4 +enforcement. This setting uses the same syntax and parent\-domain +matching behavior as mynetworks. .PP This feature is available in Postfix >= 3.9, 3.8.4, 3.7.9, 3.6.13, and 3.5.23. +.SH smtpd_forbid_bare_newline_reject_code (default: 550) +The numerical Postfix SMTP server response code when rejecting a +request with "smtpd_forbid_bare_newline = reject". +Specify a 5XX status code (521 to disconnect). +.PP +This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24. .SH smtpd_forbid_unauth_pipelining (default: Postfix >= 3.9: yes) Disconnect remote SMTP clients that violate RFC 2920 (or 5321) command pipelining constraints. The server replies with "554 5.5.0 diff --git a/postfix/man/man8/cleanup.8 b/postfix/man/man8/cleanup.8 index 8c2cc0b9e..bc51c3163 100644 --- a/postfix/man/man8/cleanup.8 +++ b/postfix/man/man8/cleanup.8 @@ -165,6 +165,14 @@ content. .IP "\fBmessage_strip_characters (empty)\fR" The set of characters that Postfix will remove from message content. +.PP +Available in Postfix version 3.9, 3.8.5, 3.7.10, 3.6.14, +3.5.24, and later: +.IP "\fBcleanup_replace_stray_cr_lf (yes)\fR" +Replace each stray or character in message +content with a space character, to prevent outbound SMTP smuggling, +and to make the evaluation of Postfix\-added DKIM or other signatures +independent from how a remote mail server handles such characters. .SH "BEFORE QUEUE MILTER CONTROLS" .na .nf diff --git a/postfix/man/man8/smtpd.8 b/postfix/man/man8/smtpd.8 index b016d9e59..6f72084a6 100644 --- a/postfix/man/man8/smtpd.8 +++ b/postfix/man/man8/smtpd.8 @@ -864,12 +864,17 @@ command pipelining constraints. .PP Available in Postfix 3.9, 3.8.4, 3.7.9, 3.6.13, 3.5.23 and later: .IP "\fBsmtpd_forbid_bare_newline (Postfix < 3.9: no)\fR" -Reply with "Error: bare received" and disconnect -when a remote SMTP client sends a line ending in , violating -the RFC 5321 requirement that lines must end in . +Reject or restrict input lines from an SMTP client that end in + instead of the standard . .IP "\fBsmtpd_forbid_bare_newline_exclusions ($mynetworks)\fR" Exclude the specified clients from smtpd_forbid_bare_newline enforcement. +.PP +Available in Postfix 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24 and +later: +.IP "\fBsmtpd_forbid_bare_newline_reject_code (550)\fR" +The numerical Postfix SMTP server response code when rejecting a +request with "smtpd_forbid_bare_newline = reject". .SH "TARPIT CONTROLS" .na .nf diff --git a/postfix/mantools/postlink b/postfix/mantools/postlink index 2a8f19564..89b0fa47d 100755 --- a/postfix/mantools/postlink +++ b/postfix/mantools/postlink @@ -557,8 +557,10 @@ while (<>) { s;\bsmtpd_etrn_restrictions\b;$&;g; s;\bsmtpd_expansion_filter\b;$&;g; s;\bsmtpd_for[-]*\n*[ ]*bidden_commands\b;$&;g; - s;\bsmtpd_for[-]*\n*[ ]*bid_bare_newline\b;$&;g; - s;\bsmtpd_for[-]*\n*[ ]*bid_bare_newline_exclusions\b;$&;g; + s;\bsmtpd_for[-]*\n*[ ]*bid_bare_new[-]*\n*[ ]*line\b;$&;g; + s;\bsmtpd_for[-]*\n*[ ]*bid_bare_new[-]*\n*[ ]*line_reject_code\b;$&;g; + s;\bsmtpd_for[-]*\n*[ ]*bid_bare_new[-]*\n*[ ]*line_exclusions\b;$&;g; + s;\bcleanup_replace_stray_cr_lf\b;$&;g; s;\bsmtpd_for[-]*\n*[ ]*bid_unauth_pipelining\b;$&;g; s;\bsmtpd_hard_error_limit\b;$&;g; s;\bsmtpd_helo_required\b;$&;g; diff --git a/postfix/proto/postconf.proto b/postfix/proto/postconf.proto index 6aa293a56..f52f37fcf 100644 --- a/postfix/proto/postconf.proto +++ b/postfix/proto/postconf.proto @@ -18721,55 +18721,169 @@ MinProtocol = TLSv1 %PARAM smtpd_forbid_bare_newline Postfix < 3.9: no -

Reply with "Error: bare <LF> received" and disconnect -when a remote SMTP client sends a line ending in <LF>, violating -the RFC 5321 requirement that lines must end in <CR><LF>. -This feature is disbled by default with Postfix < 3.9. Use -smtpd_forbid_bare_newline_exclusions to exclude non-standard clients -such as netcat. Specify "smtpd_forbid_bare_newline = no" to disable -(not recommended for an Internet-connected MTA).

+

Reject or restrict input lines from an SMTP client that end in +<LF> instead of the standard <CR><LF>. Such line +endings are commonly allowed with UNIX-based SMTP servers, but they +violate RFC 5321, and allowing such line endings can make a server +vulnerable to +SMTP smuggling.

-

See -https://www.postfix.org/smtp-smuggling.html for details. +

Specify one of the following values (case does not matter):

-

Example:

+
+ +
normalize
Require the standard +End-of-DATA sequence <CR><LF>.<CR><LF>. +Otherwise, allow command or message content lines ending in the +non-standard <LF>, and process them as if the client sent the +standard <CR><LF>.

This maintains compatibility +with many legitimate SMTP client applications that send a mix of +standard and non-standard line endings, but will fail to receive +email from client implementations that do not terminate DATA content +with the standard End-of-DATA sequence +<CR><LF>.<CR><LF>.

Such clients +can be excluded with smtpd_forbid_bare_newline_exclusions.
+ +
yes
Compatibility alias for normalize.
+ +
reject
Require the standard End-of-DATA +sequence <CR><LF>.<CR><LF>. Reject a command +or message content when a line contains bare <LF>, log a "bare +<LF> received" error, and reply with the SMTP status code in +$smtpd_forbid_bare_newline_reject_code.

This will reject +email from SMTP clients that send any non-standard line endings +such as web applications, netcat, or load balancer health checks. +

This will also reject email from services that use BDAT +to send MIME text containing a bare newline (RFC 3030 Section 3 +requires canonical MIME format for text message types, defined in +RFC 2045 Sections 2.7 and 2.8).

Such clients can be +excluded with smtpd_forbid_bare_newline_exclusions (or, in the case +of BDAT violations, BDAT can be selectively disabled with +smtpd_discard_ehlo_keyword_address_maps, or globally disabled with +smtpd_discard_ehlo_keywords).
+ +
no (default)
Do not require the standard +End-of-DATA +sequence <CR><LF>.<CR><LF>. Always process +a bare <LF> as if the client sent <CR><LF>. This +option is fully backwards compatible, but is not recommended for +an Internet-facing SMTP server, because it is vulnerable to SMTP smuggling. +
+ +
+ +

Recommended settings: 

-# Disconnect remote SMTP clients that send bare newlines, but allow
-# local clients with non-standard SMTP implementations such as netcat,
-# fax machines, or load balancer health checks.
+# Require the standard End-of-DATA sequence <CR><LF>.<CR><LF>.
+# Otherwise, allow bare <LF> and process it as if the client sent
+# <CR><LF>.
 #
-smtpd_forbid_bare_newline = yes
+# This maintains compatibility with many legitimate SMTP client
+# applications that send a mix of standard and non-standard line
+# endings, but will fail to receive email from client implementations
+# that do not terminate DATA content with the standard End-of-DATA
+# sequence <CR><LF>.<CR><LF>.
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = normalize
 smtpd_forbid_bare_newline_exclusions = $mynetworks
-

This feature is available in Postfix ≥ 3.9, 3.8.4, 3.7.9, -3.6.13, and 3.5.23.

+

Alternative:

+ +
+
+# Reject input lines that contain <LF> and log a "bare <LF> received"
+# error. Require that input lines end in <CR><LF>, and require the
+# standard End-of-DATA sequence <CR><LF>.<CR><LF>.
+#
+# This will reject email from SMTP clients that send any non-standard
+# line endings such as web applications, netcat, or load balancer
+# health checks.
+#
+# This will also reject email from services that use BDAT to send
+# MIME text containing a bare newline (RFC 3030 Section 3 requires
+# canonical MIME format for text message types, defined in RFC 2045
+# Sections 2.7 and 2.8).
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = reject
+smtpd_forbid_bare_newline_exclusions = $mynetworks
+#
+# Alternatively, in the case of BDAT violations, BDAT can be selectively
+# disabled with smtpd_discard_ehlo_keyword_address_maps, or globally
+# disabled with smtpd_discard_ehlo_keywords.
+#
+# smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file
+# /path/to/file:
+#     10.0.0.0/24 chunking, silent-discard
+# smtpd_discard_ehlo_keywords = chunking, silent-discard
+
+
+ +

This feature with settings yes and no is available +in Postfix 3.8.4, 3.7.9, 3.6.13, and 3.5.23. Additionally, the +settings reject, and normalize are available with +Postfix ≥ 3.9, 3.8.5, 3.7.10, 3.6.14, and 3.5.24.

%PARAM smtpd_forbid_bare_newline_exclusions $mynetworks

Exclude the specified clients from smtpd_forbid_bare_newline -enforcement. It uses the same syntax and parent-domain matching -behavior as mynetworks.

- -

Example:

- -
-
-# Disconnect remote SMTP clients that send bare newlines, but allow
-# local clients with non-standard SMTP implementations such as netcat,
-# fax machines, or load balancer health checks.
-#
-smtpd_forbid_bare_newline = yes
-smtpd_forbid_bare_newline_exclusions = $mynetworks
-
-
+enforcement. This setting uses the same syntax and parent-domain +matching behavior as mynetworks.

This feature is available in Postfix ≥ 3.9, 3.8.4, 3.7.9, 3.6.13, and 3.5.23.

+%PARAM smtpd_forbid_bare_newline_reject_code 550 + +

+The numerical Postfix SMTP server response code when rejecting a +request with "smtpd_forbid_bare_newline = reject". +Specify a 5XX status code (521 to disconnect). +

+ +

This feature is available in Postfix ≥ 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24.

+ +%PARAM cleanup_replace_stray_cr_lf yes + +

Replace each stray <CR> or <LF> character in message +content with a space character, to prevent outbound SMTP smuggling, +and to make the evaluation of Postfix-added DKIM or other signatures +independent from how a remote mail server handles such characters. +

+ +

SMTP does not allow such characters unless they are part of a +<CR><LF> sequence, and different mail systems handle +such stray characters in an implementation-dependent manner. Stray +<CR> or <LF> characters could be used for outbound +SMTP smuggling, where an attacker uses a Postfix server to send +message content with a non-standard End-of-DATA sequence that +triggers inbound SMTP smuggling at a remote SMTP server.

+ +

The replacement happens before all other content management, +and before Postfix may add a DKIM etc. signature; if the signature +were created first, the replacement could invalidate the signature. +

+ +

In addition to preventing SMTP smuggling, replacing stray +<CR> or <LF> characters ensures that the result of +signature validation by later mail system will not depend on how +that mail system handles those stray characters in an +implementation-dependent manner.

+ +

This feature is available in Postfix ≥ 3.9, 3.8.5, 3.7.10, +3.6.14, and 3.5.24.

+ %PARAM smtpd_forbid_unauth_pipelining Postfix ≥ 3.9: yes

Disconnect remote SMTP clients that violate RFC 2920 (or 5321) diff --git a/postfix/src/cleanup/cleanup.c b/postfix/src/cleanup/cleanup.c index 73cc03d57..6fe61f85f 100644 --- a/postfix/src/cleanup/cleanup.c +++ b/postfix/src/cleanup/cleanup.c @@ -147,6 +147,14 @@ /* .IP "\fBmessage_strip_characters (empty)\fR" /* The set of characters that Postfix will remove from message /* content. +/* .PP +/* Available in Postfix version 3.9, 3.8.5, 3.7.10, 3.6.14, +/* 3.5.24, and later: +/* .IP "\fBcleanup_replace_stray_cr_lf (yes)\fR" +/* Replace each stray or character in message +/* content with a space character, to prevent outbound SMTP smuggling, +/* and to make the evaluation of Postfix-added DKIM or other signatures +/* independent from how a remote mail server handles such characters. /* BEFORE QUEUE MILTER CONTROLS /* .ad /* .fi diff --git a/postfix/src/cleanup/cleanup_init.c b/postfix/src/cleanup/cleanup_init.c index 8c43a0212..369a019b5 100644 --- a/postfix/src/cleanup/cleanup_init.c +++ b/postfix/src/cleanup/cleanup_init.c @@ -174,6 +174,7 @@ int var_auto_8bit_enc_hdr; /* auto-detect 8bit encoding header */ int var_always_add_hdrs; /* always add missing headers */ int var_virt_addrlen_limit; /* stop exponential growth */ char *var_hfrom_format; /* header_from_format */ +int var_cleanup_mask_stray_cr_lf; /* replace stray CR or LF with space */ const CONFIG_INT_TABLE cleanup_int_table[] = { VAR_HOPCOUNT_LIMIT, DEF_HOPCOUNT_LIMIT, &var_hopcount_limit, 1, 0, @@ -190,6 +191,7 @@ const CONFIG_BOOL_TABLE cleanup_bool_table[] = { VAR_VERP_BOUNCE_OFF, DEF_VERP_BOUNCE_OFF, &var_verp_bounce_off, VAR_AUTO_8BIT_ENC_HDR, DEF_AUTO_8BIT_ENC_HDR, &var_auto_8bit_enc_hdr, VAR_ALWAYS_ADD_HDRS, DEF_ALWAYS_ADD_HDRS, &var_always_add_hdrs, + VAR_CLEANUP_MASK_STRAY_CR_LF, DEF_CLEANUP_MASK_STRAY_CR_LF, &var_cleanup_mask_stray_cr_lf, 0, }; diff --git a/postfix/src/cleanup/cleanup_message.c b/postfix/src/cleanup/cleanup_message.c index f2b86d05b..1ee0a525a 100644 --- a/postfix/src/cleanup/cleanup_message.c +++ b/postfix/src/cleanup/cleanup_message.c @@ -924,6 +924,23 @@ static void cleanup_message_headerbody(CLEANUP_STATE *state, int type, const char *cp; char *dst; + /* + * Replace each stray CR or LF with one space. These are not allowed in + * SMTP, and can be used to enable outbound (remote) SMTP smuggling. + * Replacing these early ensures that our later DKIM etc. signature will + * not be invalidated. Besides preventing SMTP smuggling, replacing stray + * or ensures that the result of signature validation by a + * later mail system will not depend on how that mail system handles + * those stray characters in an implementation-dependent manner. + * + * The input length is not changed, therefore it is safe to overwrite the + * input. + */ + if (var_cleanup_mask_stray_cr_lf) + for (dst = (char *) buf; dst < buf + len; dst++) + if (*dst == '\r' || *dst == '\n') + *dst = ' '; + /* * Reject unwanted characters. * diff --git a/postfix/src/global/cleanup_strerror.c b/postfix/src/global/cleanup_strerror.c index 74a9406da..09a06663e 100644 --- a/postfix/src/global/cleanup_strerror.c +++ b/postfix/src/global/cleanup_strerror.c @@ -73,6 +73,7 @@ static const CLEANUP_STAT_DETAIL cleanup_stat_map[] = { CLEANUP_STAT_CONT, 550, "5.7.1", "message content rejected", CLEANUP_STAT_WRITE, 451, "4.3.0", "queue file write error", CLEANUP_STAT_NOPERM, 550, "5.7.1", "service denied", + CLEANUP_STAT_BARE_LF, 521, "5.5.2", "bare received", }; static CLEANUP_STAT_DETAIL cleanup_stat_success = { diff --git a/postfix/src/global/cleanup_user.h b/postfix/src/global/cleanup_user.h index d02e9cbfe..74815bed3 100644 --- a/postfix/src/global/cleanup_user.h +++ b/postfix/src/global/cleanup_user.h @@ -64,6 +64,12 @@ #define CLEANUP_STAT_DEFER (1<<8) /* Temporary reject */ #define CLEANUP_STAT_NOPERM (1<<9) /* Denied by non-content policy */ + /* + * Non-cleanup errors that live in the same bitmask space, to centralize + * error handling. + */ +#define CLEANUP_STAT_BARE_LF (1<<16) /* Bare received */ + /* * These are set when we can't bounce even if we were asked to. */ diff --git a/postfix/src/global/mail_params.h b/postfix/src/global/mail_params.h index 1e246bcb0..3064b01c4 100644 --- a/postfix/src/global/mail_params.h +++ b/postfix/src/global/mail_params.h @@ -4282,11 +4282,18 @@ extern char *var_smtpd_dns_re_filter; * Backwards compatibility. */ #define VAR_SMTPD_FORBID_BARE_LF "smtpd_forbid_bare_newline" -#define DEF_SMTPD_FORBID_BARE_LF 0 +#define DEF_SMTPD_FORBID_BARE_LF "no" #define VAR_SMTPD_FORBID_BARE_LF_EXCL "smtpd_forbid_bare_newline_exclusions" #define DEF_SMTPD_FORBID_BARE_LF_EXCL "$" VAR_MYNETWORKS +#define VAR_SMTPD_FORBID_BARE_LF_CODE "smtpd_forbid_bare_newline_reject_code" +#define DEF_SMTPD_FORBID_BARE_LF_CODE 550 + +#define VAR_CLEANUP_MASK_STRAY_CR_LF "cleanup_replace_stray_cr_lf" +#define DEF_CLEANUP_MASK_STRAY_CR_LF 1 +extern int var_cleanup_mask_stray_cr_lf; + /* * Share TLS sessions through tlsproxy(8). */ diff --git a/postfix/src/global/mail_version.h b/postfix/src/global/mail_version.h index 39aa49c27..03f23f369 100644 --- a/postfix/src/global/mail_version.h +++ b/postfix/src/global/mail_version.h @@ -20,8 +20,8 @@ * Patches change both the patchlevel and the release date. Snapshots have no * patchlevel; they change the release date only. */ -#define MAIL_RELEASE_DATE "20231222" -#define MAIL_VERSION_NUMBER "3.8.4" +#define MAIL_RELEASE_DATE "20240121" +#define MAIL_VERSION_NUMBER "3.8.5" #ifdef SNAPSHOT #define MAIL_VERSION_DATE "-" MAIL_RELEASE_DATE diff --git a/postfix/src/global/smtp_stream.c b/postfix/src/global/smtp_stream.c index b7209009d..662950803 100644 --- a/postfix/src/global/smtp_stream.c +++ b/postfix/src/global/smtp_stream.c @@ -53,7 +53,8 @@ /* char *format; /* va_list ap; /* -/* int smtp_forbid_bare_lf; +/* int smtp_detect_bare_lf; +/* int smtp_got_bare_lf; /* AUXILIARY API /* int smtp_get_noexcept(vp, stream, maxlen, flags) /* VSTRING *vp; @@ -133,16 +134,16 @@ /* smtp_vprintf() is the machine underneath smtp_printf(). /* /* smtp_get_noexcept() implements the subset of smtp_get() -/* without long jumps for timeout or EOF errors. Instead, +/* without timeouts and without making long jumps. Instead, /* query the stream status with vstream_feof() etc. -/* This function will make a VSTREAM long jump (error code -/* SMTP_ERR_LF) when rejecting input with a bare newline byte. +/* +/* This function assigns smtp_got_bare_lf = smtp_detect_bare_lf, +/* if smtp_detect_bare_lf is non-zero and the last read line +/* was terminated with a bare newline. Otherwise, this function +/* sets smtp_got_bare_lf to zero. /* /* smtp_timeout_setup() is a backwards-compatibility interface /* for programs that don't require deadline or data-rate support. -/* -/* smtp_forbid_bare_lf controls whether smtp_get_noexcept() -/* will reject input with a bare newline byte. /* DIAGNOSTICS /* .fi /* .ad @@ -221,7 +222,8 @@ * the buffer. Such system calls would really hurt when receiving or sending * body content one line at a time. */ -int smtp_forbid_bare_lf; +int smtp_detect_bare_lf; +int smtp_got_bare_lf; /* smtp_timeout_reset - reset per-stream error flags */ @@ -384,6 +386,8 @@ int smtp_get_noexcept(VSTRING *vp, VSTREAM *stream, ssize_t bound, int flags int last_char; int next_char; + smtp_got_bare_lf = 0; + /* * It's painful to do I/O with records that may span multiple buffers. * Allow for partial long lines (we will read the remainder later) and @@ -426,11 +430,15 @@ int smtp_get_noexcept(VSTRING *vp, VSTREAM *stream, ssize_t bound, int flags */ case '\n': vstring_truncate(vp, VSTRING_LEN(vp) - 1); - if (smtp_forbid_bare_lf - && (VSTRING_LEN(vp) == 0 || vstring_end(vp)[-1] != '\r')) - vstream_longjmp(stream, SMTP_ERR_LF); - while (VSTRING_LEN(vp) > 0 && vstring_end(vp)[-1] == '\r') - vstring_truncate(vp, VSTRING_LEN(vp) - 1); + if (smtp_detect_bare_lf) { + if (VSTRING_LEN(vp) == 0 || vstring_end(vp)[-1] != '\r') + smtp_got_bare_lf = smtp_detect_bare_lf; + else + vstring_truncate(vp, VSTRING_LEN(vp) - 1); + } else { + while (VSTRING_LEN(vp) > 0 && vstring_end(vp)[-1] == '\r') + vstring_truncate(vp, VSTRING_LEN(vp) - 1); + } VSTRING_TERMINATE(vp); /* FALLTRHOUGH */ diff --git a/postfix/src/global/smtp_stream.h b/postfix/src/global/smtp_stream.h index 4bcd6b59b..2cf011a55 100644 --- a/postfix/src/global/smtp_stream.h +++ b/postfix/src/global/smtp_stream.h @@ -32,7 +32,6 @@ #define SMTP_ERR_QUIET 3 /* silent cleanup (application) */ #define SMTP_ERR_NONE 4 /* non-error case */ #define SMTP_ERR_DATA 5 /* application data error */ -#define SMTP_ERR_LF 6 /* bare protocol error */ extern void smtp_stream_setup(VSTREAM *, int, int, int); extern void PRINTFLIKE(2, 3) smtp_printf(VSTREAM *, const char *,...); @@ -44,7 +43,8 @@ extern void smtp_fputs(const char *, ssize_t len, VSTREAM *); extern void smtp_fwrite(const char *, ssize_t len, VSTREAM *); extern void smtp_fread_buf(VSTRING *, ssize_t len, VSTREAM *); extern void smtp_fputc(int, VSTREAM *); -extern int smtp_forbid_bare_lf; +extern int smtp_detect_bare_lf; +extern int smtp_got_bare_lf; extern void smtp_vprintf(VSTREAM *, const char *, va_list); diff --git a/postfix/src/smtpd/smtpd.c b/postfix/src/smtpd/smtpd.c index 38c0cf07f..e84128b0d 100644 --- a/postfix/src/smtpd/smtpd.c +++ b/postfix/src/smtpd/smtpd.c @@ -818,12 +818,17 @@ /* .PP /* Available in Postfix 3.9, 3.8.4, 3.7.9, 3.6.13, 3.5.23 and later: /* .IP "\fBsmtpd_forbid_bare_newline (Postfix < 3.9: no)\fR" -/* Reply with "Error: bare received" and disconnect -/* when a remote SMTP client sends a line ending in , violating -/* the RFC 5321 requirement that lines must end in . +/* Reject or restrict input lines from an SMTP client that end in +/* instead of the standard . /* .IP "\fBsmtpd_forbid_bare_newline_exclusions ($mynetworks)\fR" /* Exclude the specified clients from smtpd_forbid_bare_newline /* enforcement. +/* .PP +/* Available in Postfix 3.9, 3.8.5, 3.7.10, 3.6.14, 3.5.24 and +/* later: +/* .IP "\fBsmtpd_forbid_bare_newline_reject_code (550)\fR" +/* The numerical Postfix SMTP server response code when rejecting a +/* request with "smtpd_forbid_bare_newline = reject". /* TARPIT CONTROLS /* .ad /* .fi @@ -1534,8 +1539,10 @@ bool var_relay_before_rcpt_checks; bool var_smtpd_req_deadline; int var_smtpd_min_data_rate; char *var_hfrom_format; -bool var_smtpd_forbid_bare_lf; +char *var_smtpd_forbid_bare_lf; char *var_smtpd_forbid_bare_lf_excl; +int var_smtpd_forbid_bare_lf_code; +static int bare_lf_mask; static NAMADR_LIST *bare_lf_excl; /* @@ -1612,7 +1619,6 @@ static void tls_reset(SMTPD_STATE *); #define REASON_TIMEOUT "timeout" #define REASON_LOST_CONNECTION "lost connection" #define REASON_ERROR_LIMIT "too many errors" -#define REASON_BARE_LF "bare received" #ifdef USE_TLS @@ -1636,6 +1642,40 @@ static DICT *smtpd_cmd_filter; */ int smtpd_hfrom_format; + /* + * Bare LF and End-of-DATA controls (bare CR is handled elsewhere). + * + * At the smtp_get*() line reader level, setting any of these flags in the + * smtp_detect_bare_lf variable enables the detection of bare newlines. The + * line reader will set the same flags in the smtp_got_bare_lf variable + * after it detects a bare newline, otherwise it clears smtp_got_bare_lf. + * + * At the SMTP command level, the flags in smtp_got_bare_lf control whether + * commands ending in a bare newline are rejected. + * + * At the DATA and BDAT content level, the flags in smtp_got_bare_lf control + * whether the standard End-of-DATA sequence CRLF.CRLF is required, and + * whether lines ending in bare newlines are rejected. + * + * Postfix implements "delayed reject" after detecting a bare newline in BDAT + * or DATA content. The SMTP server delays a REJECT response until the + * command is finished, instead of replying and hanging up immediately. The + * End-of-DATA detection is secured with BARE_LF_FLAG_WANT_STD_EOD. + */ +#define BARE_LF_FLAG_WANT_STD_EOD (1<<0) /* Require CRLF.CRLF */ +#define BARE_LF_FLAG_REPLY_REJECT (1<<1) /* Reject bare newline */ + +#define IS_BARE_LF_WANT_STD_EOD(m) ((m) & BARE_LF_FLAG_WANT_STD_EOD) +#define IS_BARE_LF_REPLY_REJECT(m) ((m) & BARE_LF_FLAG_REPLY_REJECT) + +static const NAME_CODE bare_lf_mask_table[] = { + "normalize", BARE_LF_FLAG_WANT_STD_EOD, /* Default */ + "yes", BARE_LF_FLAG_WANT_STD_EOD, /* Migration aid */ + "reject", BARE_LF_FLAG_WANT_STD_EOD | BARE_LF_FLAG_REPLY_REJECT, + "no", 0, + 0, -1, /* error */ +}; + #ifdef USE_SASL_AUTH /* @@ -3578,6 +3618,7 @@ static void receive_data_message(SMTPD_STATE *state, int curr_rec_type; int prev_rec_type; int first = 1; + int prev_got_bare_lf = 0; /* * If deadlines are enabled, increase the time budget as message content @@ -3598,12 +3639,15 @@ static void receive_data_message(SMTPD_STATE *state, * XXX Deal with UNIX-style From_ lines at the start of message content * because sendmail permits it. */ - for (prev_rec_type = 0; /* void */ ; prev_rec_type = curr_rec_type) { + for (prev_rec_type = 0; /* void */ ; prev_rec_type = curr_rec_type, + prev_got_bare_lf = smtp_got_bare_lf) { if (smtp_get(state->buffer, state->client, var_line_limit, SMTP_GET_FLAG_NONE) == '\n') curr_rec_type = REC_TYPE_NORM; else curr_rec_type = REC_TYPE_CONT; + if (IS_BARE_LF_REPLY_REJECT(smtp_got_bare_lf)) + state->err |= CLEANUP_STAT_BARE_LF; start = vstring_str(state->buffer); len = VSTRING_LEN(state->buffer); if (first) { @@ -3616,9 +3660,14 @@ static void receive_data_message(SMTPD_STATE *state, if (len > 0 && IS_SPACE_TAB(start[0])) out_record(out_stream, REC_TYPE_NORM, "", 0); } - if (prev_rec_type != REC_TYPE_CONT && *start == '.' - && (proxy == 0 ? (++start, --len) == 0 : len == 1)) - break; + if (prev_rec_type != REC_TYPE_CONT && *start == '.') { + if (len == 1 && IS_BARE_LF_WANT_STD_EOD(smtp_detect_bare_lf) + && (smtp_got_bare_lf || prev_got_bare_lf)) + /* Do not store or send to proxy filter. */ + continue; + if (proxy == 0 ? (++start, --len) == 0 : len == 1) + break; + } if (state->err == CLEANUP_STAT_OK) { if (ENFORCING_SIZE_LIMIT(var_message_limit) && var_message_limit - state->act_size < len + 2) { @@ -3771,6 +3820,11 @@ static int common_post_message_handling(SMTPD_STATE *state) else smtpd_chat_reply(state, "250 2.0.0 Ok: queued as %s", state->queue_id); + } else if ((state->err & CLEANUP_STAT_BARE_LF) != 0) { + state->error_mask |= MAIL_ERROR_PROTOCOL; + log_whatsup(state, "reject", "bare received"); + smtpd_chat_reply(state, "%d 5.5.2 %s Error: bare received", + var_smtpd_forbid_bare_lf_code, var_myhostname); } else if (why && IS_SMTP_REJECT(STR(why))) { state->error_mask |= MAIL_ERROR_POLICY; smtpd_chat_reply(state, "%s", STR(why)); @@ -4058,7 +4112,6 @@ static int bdat_cmd(SMTPD_STATE *state, int argc, SMTPD_TOKEN *argv) */ done = 0; do { - int payload_err; /* * Do not skip the smtp_fread_buf() call if read_len == 0. We still @@ -4072,10 +4125,6 @@ static int bdat_cmd(SMTPD_STATE *state, int argc, SMTPD_TOKEN *argv) smtp_fread_buf(state->buffer, read_len, state->client); state->bdat_get_stream = vstream_memreopen( state->bdat_get_stream, state->buffer, O_RDONLY); - vstream_control(state->bdat_get_stream, CA_VSTREAM_CTL_EXCEPT, - CA_VSTREAM_CTL_END); - if ((payload_err = vstream_setjmp(state->bdat_get_stream)) != 0) - vstream_longjmp(state->client, payload_err); /* * Read lines from the fragment. The last line may continue in the @@ -4100,6 +4149,8 @@ static int bdat_cmd(SMTPD_STATE *state, int argc, SMTPD_TOKEN *argv) /* Skip the out_record() and VSTRING_RESET() calls below. */ break; } + if (IS_BARE_LF_REPLY_REJECT(smtp_got_bare_lf)) + state->err |= CLEANUP_STAT_BARE_LF; start = vstring_str(state->bdat_get_buffer); len = VSTRING_LEN(state->bdat_get_buffer); if (state->err == CLEANUP_STAT_OK) { @@ -4751,9 +4802,9 @@ static int xclient_cmd(SMTPD_STATE *state, int argc, SMTPD_TOKEN *argv) */ xclient_allowed = namadr_list_match(xclient_hosts, state->name, state->addr); - smtp_forbid_bare_lf = SMTPD_STAND_ALONE((state)) == 0 - && var_smtpd_forbid_bare_lf - && !namadr_list_match(bare_lf_excl, state->name, state->addr); + smtp_detect_bare_lf = (SMTPD_STAND_ALONE((state)) == 0 && bare_lf_mask + && !namadr_list_match(bare_lf_excl, state->name, state->addr)) ? + bare_lf_mask : 0; /* NOT: tls_reset() */ if (got_helo == 0) helo_reset(state); @@ -5575,13 +5626,6 @@ static void smtpd_proto(SMTPD_STATE *state) var_myhostname); break; - case SMTP_ERR_LF: - state->reason = REASON_BARE_LF; - if (vstream_setjmp(state->client) == 0) - smtpd_chat_reply(state, "521 5.5.2 %s Error: bare received", - var_myhostname); - break; - case 0: /* @@ -5801,6 +5845,13 @@ static void smtpd_proto(SMTPD_STATE *state) } watchdog_pat(); smtpd_chat_query(state); + if (IS_BARE_LF_REPLY_REJECT(smtp_got_bare_lf)) { + log_whatsup(state, "reject", "bare received"); + state->error_mask |= MAIL_ERROR_PROTOCOL; + smtpd_chat_reply(state, "%d 5.5.2 %s Error: bare received", + var_smtpd_forbid_bare_lf_code, var_myhostname); + break; + } /* Safety: protect internal interfaces against malformed UTF-8. */ if (var_smtputf8_enable && valid_utf8_string(STR(state->buffer), LEN(state->buffer)) == 0) { @@ -6150,11 +6201,11 @@ static void smtpd_service(VSTREAM *stream, char *service, char **argv) namadr_list_match(xforward_hosts, state.name, state.addr); /* - * Enforce strict SMTP line endings, with compatibility exclusions. + * Reject or normalize bare LF, with compatibility exclusions. */ - smtp_forbid_bare_lf = SMTPD_STAND_ALONE((&state)) == 0 - && var_smtpd_forbid_bare_lf - && !namadr_list_match(bare_lf_excl, state.name, state.addr); + smtp_detect_bare_lf = (SMTPD_STAND_ALONE((&state)) == 0 && bare_lf_mask + && !namadr_list_match(bare_lf_excl, state.name, state.addr)) ? + bare_lf_mask : 0; /* * See if we need to turn on verbose logging for this client. @@ -6221,6 +6272,10 @@ static void pre_jail_init(char *unused_name, char **unused_argv) MATCH_FLAG_RETURN | match_parent_style(VAR_MYNETWORKS), var_smtpd_forbid_bare_lf_excl); + if ((bare_lf_mask = name_code(bare_lf_mask_table, NAME_CODE_FLAG_NONE, + var_smtpd_forbid_bare_lf)) < 0) + msg_fatal("bad parameter value: '%s = %s'", + VAR_SMTPD_FORBID_BARE_LF, var_smtpd_forbid_bare_lf); /* * Open maps before dropping privileges so we can read passwords etc. @@ -6521,6 +6576,7 @@ int main(int argc, char **argv) VAR_VIRT_MAILBOX_CODE, DEF_VIRT_MAILBOX_CODE, &var_virt_mailbox_code, 0, 0, VAR_RELAY_RCPT_CODE, DEF_RELAY_RCPT_CODE, &var_relay_rcpt_code, 0, 0, VAR_PLAINTEXT_CODE, DEF_PLAINTEXT_CODE, &var_plaintext_code, 0, 0, + VAR_SMTPD_FORBID_BARE_LF_CODE, DEF_SMTPD_FORBID_BARE_LF_CODE, &var_smtpd_forbid_bare_lf_code, 500, 599, VAR_SMTPD_CRATE_LIMIT, DEF_SMTPD_CRATE_LIMIT, &var_smtpd_crate_limit, 0, 0, VAR_SMTPD_CCONN_LIMIT, DEF_SMTPD_CCONN_LIMIT, &var_smtpd_cconn_limit, 0, 0, VAR_SMTPD_CMAIL_LIMIT, DEF_SMTPD_CMAIL_LIMIT, &var_smtpd_cmail_limit, 0, 0, @@ -6587,7 +6643,6 @@ int main(int argc, char **argv) VAR_SMTPD_DELAY_OPEN, DEF_SMTPD_DELAY_OPEN, &var_smtpd_delay_open, VAR_SMTPD_CLIENT_PORT_LOG, DEF_SMTPD_CLIENT_PORT_LOG, &var_smtpd_client_port_log, VAR_SMTPD_FORBID_UNAUTH_PIPE, DEF_SMTPD_FORBID_UNAUTH_PIPE, &var_smtpd_forbid_unauth_pipe, - VAR_SMTPD_FORBID_BARE_LF, DEF_SMTPD_FORBID_BARE_LF, &var_smtpd_forbid_bare_lf, 0, }; static const CONFIG_NBOOL_TABLE nbool_table[] = { @@ -6705,6 +6760,7 @@ int main(int argc, char **argv) VAR_SMTPD_REJ_FTR_MAPS, DEF_SMTPD_REJ_FTR_MAPS, &var_smtpd_rej_ftr_maps, 0, 0, VAR_HFROM_FORMAT, DEF_HFROM_FORMAT, &var_hfrom_format, 1, 0, VAR_SMTPD_FORBID_BARE_LF_EXCL, DEF_SMTPD_FORBID_BARE_LF_EXCL, &var_smtpd_forbid_bare_lf_excl, 0, 0, + VAR_SMTPD_FORBID_BARE_LF, DEF_SMTPD_FORBID_BARE_LF, &var_smtpd_forbid_bare_lf, 1, 0, 0, }; static const CONFIG_RAW_TABLE raw_table[] = { diff --git a/postfix/src/smtpd/smtpd_check.c b/postfix/src/smtpd/smtpd_check.c index b5ce4a94f..7212ccf89 100644 --- a/postfix/src/smtpd/smtpd_check.c +++ b/postfix/src/smtpd/smtpd_check.c @@ -48,6 +48,11 @@ /* /* char *smtpd_check_queue(state) /* SMTPD_STATE *state; +/* AUXILIARY FUNCTIONS +/* void log_whatsup(state, action, text) +/* SMTPD_STATE *state; +/* const char *action; +/* const char *text; /* DESCRIPTION /* This module implements additional checks on SMTP client requests. /* A client request is validated in the context of the session state. @@ -146,6 +151,11 @@ /* The recipient address given with the RCPT TO or VRFY command. /* .IP size /* The message size given with the MAIL FROM command (zero if unknown). +/* .PP +/* log_whatsup() logs ": : +/* from: : " plus the protocol +/* (SMTP or ESMTP), and if available, EHLO, MAIL FROM, or RCPT +/* TO. /* BUGS /* Policies like these should not be hard-coded in C, but should /* be user-programmable instead. @@ -988,8 +998,8 @@ void smtpd_check_init(void) /* log_whatsup - log as much context as we have */ -static void log_whatsup(SMTPD_STATE *state, const char *whatsup, - const char *text) +void log_whatsup(SMTPD_STATE *state, const char *whatsup, + const char *text) { VSTRING *buf = vstring_alloc(100); diff --git a/postfix/src/smtpd/smtpd_check.h b/postfix/src/smtpd/smtpd_check.h index ce24498e2..bf0fe001a 100644 --- a/postfix/src/smtpd/smtpd_check.h +++ b/postfix/src/smtpd/smtpd_check.h @@ -25,6 +25,7 @@ extern char *smtpd_check_etrn(SMTPD_STATE *, char *); extern char *smtpd_check_data(SMTPD_STATE *); extern char *smtpd_check_eod(SMTPD_STATE *); extern char *smtpd_check_policy(SMTPD_STATE *, char *); +extern void log_whatsup(SMTPD_STATE *, const char *, const char *); /* LICENSE /* .ad