≡ Menu

domain name system

BIND 9 Dynamic Update DoS Security Update

BIND 9 is an implementation of the Domain Name System (DNS) protocols. named daemon is an Internet Domain Name Server for UNIX like operating systems. Dynamic update messages may be used to update records in a master zone on a nameserver. When named receives a specially crafted dynamic update message an internal assertion check is triggered which causes named to exit. An attacker which can send DNS requests to a nameserver can cause it to exit, thus creating a Denial of Service situation. configuring named to ignore dynamic updates is NOT sufficient to protect it from this vulnerability. This exploit is public. Please upgrade immediately.
[click to continue…]

Updated kernel packages that fix several bugs, while adding an enhancement are now available for Red Hat Enterprise Linux 4.

The kernel packages contain the Linux kernel, the core of any Linux operating system.

These updated packages fix the following bugs:

* the GNU libc stub resolver is a minimal resolver that works with Domain Name System (DNS) servers to satisfy requests from applications for names. The GNU libc stub resolver did not specify a source UDP port, and therefore used predictable port numbers. This could have make DNS spoofing attacks easier.

The Linux kernel has been updated to implement random UDP source ports where none are specified by an application. This allows applications, such as those using the GNU libc stub resolver, to use random UDP source ports, helping to make DNS spoofing attacks harder.

* A set of patches detailed as "sys_times: Fix system unresponsiveness during many concurrent invocation of sys_times()" and "Minor code cleanup to sys_times() call" introduced regression which caused a kernel panic under high load. These patches were reverted in the current release.

* A process could hang in an uninterruptible state while accessing application data files due to race condition in asynchronous direct I/O system calls.

* USB devices would not be detected on a PowerEdge R805 system. USB devices are now able to be detected on the aforementioned system with this update.

Further, these updated packages add the following enhancement:

* Added HDMI support for AMD ATI chipsets RS780, RV610, RV620, RV630, RV635, RV670 and RV770.

How do I upgrade my kernel on RHEL 4.x?

Type the following command as root user:
# up2date -uf

I. Background
BIND 9 is an implementation of the Domain Name System (DNS) protocols.
The named(8) daemon is an Internet Domain Name Server. DNS requests
contain a query id which is used to match a DNS request with the response
and to make it harder for anybody but the DNS server which received the
request to send a valid response.

II. Problem Description

The BIND DNS implementation does not randomize the UDP source port when
doing remote queries, and the query id alone does not provide adequate

III. Impact

The lack of source port randomization reduces the amount of data the
attacker needs to guess in order to successfully execute a DNS cache
poisoning attack. This allows the attacker to influence or control
the results of DNS queries being returned to users from target systems.

IV. Workaround

Limiting the group of machines that can do recursive queries on the DNS
server will make it more difficult, but not impossible, for this
vulnerability to be exploited.

To limit the machines able to perform recursive queries, add an ACL in
named.conf and limit recursion like the following:

acl example-acl {;

options {
recursion yes;
allow-recursion { example-acl; };

V. Solution

Perform one of the following:

1) Upgrade your vulnerable system to 6-STABLE or 7-STABLE, or to the
RELENG_7_0 or RELENG_6_3 security branch dated after the correction

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 6.3 and
7.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

[FreeBSD 6.3]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind63.patch.asc

[FreeBSD 7.0]
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch
# fetch http://security.FreeBSD.org/patches/SA-08:06/bind7.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch # cd /usr/src/lib/bind # make obj && make depend && make && make install # cd /usr/src/usr.sbin/named # make obj && make depend && make && make install

NOTE WELL: This update causes BIND to choose a new, random UDP port for
each new query; this may cause problems for some network configurations,
particularly if firewall(s) block incoming UDP packets on particular
ports. The avoid-v4-udp-ports and avoid-v6-udp-ports options should be
used to avoid selecting random port numbers within a blocked range.

NOTE WELL: If a port number is specified via the query-source or
query-source-v6 options to BIND, randomized port selection will not be
used. Consequently it is strongly recommended that these options not
be used to specify fixed port numbers.

The latest revision of this advisory is available at FreeBSD