From 7c2136766bbe2cbdc1451a91ea5f178b13fad56c Mon Sep 17 00:00:00 2001 From: Suzanne Goldlust Date: Mon, 1 Jun 2020 14:46:24 +0000 Subject: [PATCH] Content, grammar, and clarity updates to security.rst --- doc/arm/security.rst | 114 +++++++++++++++++++++---------------------- 1 file changed, 57 insertions(+), 57 deletions(-) diff --git a/doc/arm/security.rst b/doc/arm/security.rst index 015604c26f..7a76aef44d 100644 --- a/doc/arm/security.rst +++ b/doc/arm/security.rst @@ -28,18 +28,18 @@ BIND 9 Security Considerations Access Control Lists -------------------- -Access Control Lists (ACLs) are address match lists that you can set up -and nickname for future use in ``allow-notify``, ``allow-query``, +Access Control Lists (ACLs) are address match lists that can be set up +and nicknamed for future use in ``allow-notify``, ``allow-query``, ``allow-query-on``, ``allow-recursion``, ``blackhole``, ``allow-transfer``, ``match-clients``, etc. -Using ACLs allows you to have finer control over who can access your -name server, without cluttering up your config files with huge lists of +ACLs give users finer control over who can access the +name server, without cluttering up config files with huge lists of IP addresses. -It is a *good idea* to use ACLs, and to control access to your server. -Limiting access to your server by outside parties can help prevent -spoofing and denial of service (DoS) attacks against your server. +It is a *good idea* to use ACLs, and to control access. +Limiting access to the server by outside parties can help prevent +spoofing and denial of service (DoS) attacks against the server. ACLs match clients on the basis of up to three characteristics: 1) The client's IP address; 2) the TSIG or SIG(0) key that was used to sign the @@ -50,7 +50,7 @@ Here is an example of ACLs based on client addresses: :: - // Set up an ACL named "bogusnets" that will block + // Set up an ACL named "bogusnets" that blocks // RFC1918 space and some reserved space, which is // commonly used in spoofing attacks. acl bogusnets { @@ -77,9 +77,9 @@ Here is an example of ACLs based on client addresses: allow-query { any; }; }; -This allows authoritative queries for "example.com" from any address, -but recursive queries only from the networks specified in "our-nets", -and no queries at all from the networks specified in "bogusnets". +This allows authoritative queries for ``example.com`` from any address, +but recursive queries only from the networks specified in ``our-nets``, +and no queries at all from the networks specified in ``bogusnets``. In addition to network addresses and prefixes, which are matched against the source address of the DNS request, ACLs may include ``key`` @@ -87,32 +87,32 @@ elements, which specify the name of a TSIG or SIG(0) key. When BIND 9 is built with GeoIP support, ACLs can also be used for geographic access restrictions. This is done by specifying an ACL -element of the form: ``geoip db database field value`` +element of the form: ``geoip db database field value``. -The ``field`` indicates which field to search for a match. Available fields -are "country", "region", "city", "continent", "postal" (postal code), -"metro" (metro code), "area" (area code), "tz" (timezone), "isp", -"asnum", and "domain". +The ``field`` parameter indicates which field to search for a match. Available fields +are ``country``, ``region``, ``city``, ``continent``, ``postal`` (postal code), +``metro`` (metro code), ``area`` (area code), ``tz`` (timezone), ``isp``, +``asnum``, and ``domain``. ``value`` is the value to search for within the database. A string may be quoted -if it contains spaces or other special characters. An "asnum" search for +if it contains spaces or other special characters. An ``asnum`` search for autonomous system number can be specified using the string "ASNNNN" or the -integer NNNN. When "country" search is specified with a string is two characters -long, then it must be a standard ISO-3166-1 two-letter country code; otherwise -it is interpreted as the full name of the country. Similarly, if this is a -"region" search and the string is two characters long, then it treated as a -standard two-letter state or province abbreviation; otherwise it treated as the +integer NNNN. If a ``country`` search is specified with a string that is two characters +long, it must be a standard ISO-3166-1 two-letter country code; otherwise +it is interpreted as the full name of the country. Similarly, if +``region`` is the search term and the string is two characters long, it is treated as a +standard two-letter state or province abbreviation; otherwise, it is treated as the full name of the state or province. -The ``database`` field indicates which GeoIP database to search for a match. In +The ``database`` field indicates which GeoIP database to search for a match. In most cases this is unnecessary, because most search fields can only be found in -a single database. However, searches for "continent" or "country" can be -answered from either the "city" or "country" databases, so for these search -types, specifying a ``database`` will force the query to be answered from that -database and no other. If ``database`` is not specified, then these queries -will be answered from the "city", database if it is installed, or the "country" -database if it is installed, in that order. Valid database names are "country", -"city", "asnum", "isp", and "domain". +a single database. However, searches for ``continent`` or ``country`` can be +answered from either the ``city`` or ``country`` databases, so for these search +types, specifying a ``database`` forces the query to be answered from that +database and no other. If a ``database`` is not specified, these queries +are first answered from the ``city`` database if it is installed, and then from the ``country`` +database if it is installed. Valid database names are ``country``, +``city``, ``asnum``, ``isp``, and ``domain``. Some example GeoIP ACLs: @@ -132,11 +132,11 @@ ACLs use a "first-match" logic rather than "best-match": if an address prefix matches an ACL element, then that ACL is considered to have matched even if a later element would have matched more specifically. For example, the ACL ``{ 10/8; !10.0.0.1; }`` would actually match a -query from 10.0.0.1, because the first element indicated that the query +query from 10.0.0.1, because the first element indicates that the query should be accepted, and the second element is ignored. When using "nested" ACLs (that is, ACLs included or referenced within -other ACLs), a negative match of a nested ACL will the containing ACL to +other ACLs), a negative match of a nested ACL tells the containing ACL to continue looking for matches. This enables complex ACLs to be constructed, in which multiple client characteristics can be checked at the same time. For example, to construct an ACL which allows queries @@ -148,11 +148,11 @@ signed with a particular key, use: allow-query { !{ !10/8; any; }; key example; }; Within the nested ACL, any address that is *not* in the 10/8 network -prefix will be rejected, and this will terminate processing of the ACL. -Any address that *is* in the 10/8 network prefix will be accepted, but +prefix is rejected, which terminates processing of the ACL. +Any address that *is* in the 10/8 network prefix is accepted, but this causes a negative match of the nested ACL, so the containing ACL -continues processing. The query will then be accepted if it is signed by -the key "example", and rejected otherwise. The ACL, then, will only +continues processing. The query is accepted if it is signed by +the key ``example``, and rejected otherwise. The ACL, then, only matches when *both* conditions are true. .. _chroot_and_setuid: @@ -160,12 +160,12 @@ matches when *both* conditions are true. ``Chroot`` and ``Setuid`` ------------------------- -On UNIX servers, it is possible to run BIND in a *chrooted* environment +On Unix servers, it is possible to run BIND in a *chrooted* environment (using the ``chroot()`` function) by specifying the ``-t`` option for ``named``. This can help improve system security by placing BIND in a -"sandbox", which will limit the damage done if a server is compromised. +"sandbox," which limits the damage done if a server is compromised. -Another useful feature in the UNIX version of BIND is the ability to run +Another useful feature in the Unix version of BIND is the ability to run the daemon as an unprivileged user ( ``-u`` user ). We suggest running as an unprivileged user when using the ``chroot`` feature. @@ -179,17 +179,17 @@ Here is an example command line to load BIND in a ``chroot`` sandbox, The ``chroot`` Environment ~~~~~~~~~~~~~~~~~~~~~~~~~~ -In order for a ``chroot`` environment to work properly in a particular -directory (for example, ``/var/named``), you will need to set up an -environment that includes everything BIND needs to run. From BIND's -point of view, ``/var/named`` is the root of the filesystem. You will -need to adjust the values of options like ``directory`` and ``pid-file`` -to account for this. +For a ``chroot`` environment to work properly in a particular +directory (for example, ``/var/named``), the +environment must include everything BIND needs to run. From BIND's +point of view, ``/var/named`` is the root of the filesystem; +the values of options like ``directory`` and ``pid-file`` +must be adjusted to account for this. -Unlike with earlier versions of BIND, you typically will *not* need to -compile ``named`` statically nor install shared libraries under the new -root. However, depending on your operating system, you may need to set -up things like ``/dev/zero``, ``/dev/random``, ``/dev/log``, and +Unlike with earlier versions of BIND, +``named`` does *not* typically need to be compiled statically, nor do shared libraries need to be installed under the new +root. However, depending on the operating system, it may be necessary to set +up locations such as ``/dev/zero``, ``/dev/random``, ``/dev/log``, and ``/etc/localtime``. .. _setuid: @@ -199,13 +199,13 @@ Using the ``setuid`` Function Prior to running the ``named`` daemon, use the ``touch`` utility (to change file access and modification times) or the ``chown`` utility (to -set the user id and/or group id) on files to which you want BIND to +set the user id and/or group id) on files where BIND should write. .. note:: - If the ``named`` daemon is running as an unprivileged user, it will - not be able to bind to new restricted ports if the server is + If the ``named`` daemon is running as an unprivileged user, it + cannot bind to new restricted ports if the server is reloaded. .. _dynamic_update_security: @@ -219,10 +219,10 @@ address of the host requesting the update, by listing an IP address or network prefix in the ``allow-update`` zone option. This method is insecure since the source address of the update UDP packet is easily forged. Also note that if the IP addresses allowed by the -``allow-update`` option include the address of a slave server which -performs forwarding of dynamic updates, the master can be trivially -attacked by sending the update to the slave, which will forward it to -the master with its own source IP address causing the master to approve +``allow-update`` option include the address of a secondary server which +performs forwarding of dynamic updates, the primary can be trivially +attacked by sending the update to the secondary, which forwards it to +the primary with its own source IP address - causing the primary to approve it without question. For these reasons, we strongly recommend that updates be @@ -234,4 +234,4 @@ names, not IP addresses or network prefixes. Alternatively, the new Some sites choose to keep all dynamically-updated DNS data in a subdomain and delegate that subdomain to a separate zone. This way, the top-level zone containing critical data such as the IP addresses of -public web and mail servers need not allow dynamic update at all. +public web and mail servers need not allow dynamic updates at all.