Subject: Multiple Remote Vulnerabilities in BIND4 and BIND8
To: None <>
From: Wolfgang Rupprecht <>
List: netbsd-users
Date: 11/12/2002 12:04:33
I haven't seen this posted yet, but it sounds important. -wsr



Internet Security Systems Security Advisory
November 12, 2002

Multiple Remote Vulnerabilities in BIND4 and BIND8


ISS X-Force has discovered several serious vulnerabilities in the Berkeley
Internet Name Domain Server (BIND). BIND is the most common implementation of
the DNS (Domain Name Service) protocol, which is used on the vast majority of
DNS servers on the Internet. DNS is a vital Internet protocol that maintains
a database of easy-to-remember domain names (host names) and their
corresponding numerical IP addresses.


The vulnerabilities described in this advisory affect nearly all currently
deployed recursive DNS servers on the Internet. The DNS network is considered
a critical component of Internet infrastructure. There is no information
implying that these exploits are known to the computer underground, and there
are no reports of active attacks. If exploits for these vulnerabilities are
developed and made public, they may lead to compromise and DoS attacks against
vulnerable DNS servers. Since the vulnerability is widespread, an Internet
worm may be developed to propagate by exploiting the flaws in BIND. Widespread
attacks against the DNS system may lead to general instability and inaccuracy
of DNS data.

Affected Versions:

BIND SIG Cached RR Overflow Vulnerability

    BIND 8, versions up to and including 8.3.3-REL
    BIND 4, versions up to and including 4.9.10-REL


    BIND 8, versions 8.3.0 up to and including 8.3.3-REL

BIND SIG Expiry Time DoS

    BIND 8, versions up to and including 8.3.3-REL


BIND SIG Cached RR Overflow Vulnerability

A buffer overflow exists in BIND 4 and 8 that may lead to remote compromise of
vulnerable DNS servers. An attacker who controls any authoritative DNS server
may cause BIND to cache DNS information within its internal database, if
recursion is enabled. Recursion is enabled by default unless explicitly
disabled via command line options or in the BIND configuration file. Attackers
must either create their own name server that is authoritative for any domain,
or compromise any other authoritative server with the same criteria. Cached
information is retrieved when requested by a DNS client. There is a flaw in
the formation of DNS responses containing SIG resource records (RR) that can
lead to buffer overflow and execution of arbitrary code.


Recursive BIND 8 servers can be caused to abruptly terminate due to an
assertion failure. A client requesting a DNS lookup on a nonexistent sub-
domain of a valid domain name may cause BIND 8 to terminate by attaching an
OPT resource record with a large UDP payload size. This DoS may also be
triggered for queries on domains whose authoritative DNS servers are

BIND SIG Expiry Time DoS

Recursive BIND 8 servers can be caused to abruptly terminate due to a null
pointer dereference. An attacker who controls any authoritative name server
may cause vulnerable BIND 8 servers to attempt to cache SIG RR elements with
invalid expiry times. These are removed from the BIND internal database, but
later improperly referenced, leading to a DoS condition.


ISS X-Force recommends that system administrators immediately take steps to
protect their networks. ISS has made several product updates available to
assess vulnerability to this issue as well as protect customers from
exploitation attempts.

The following ISS updates and product releases address the issues described
in this advisory. These updates are available from the ISS Download Center

RealSecure Network Sensor XPU 20.7 and XPU 5.6
Internet Scanner XPU 6.20
RealSecure Guard 3.1 ebs
RealSecure Sentry 3.1 ebs
RealSecure Server Sensor 6.5 SR 3.3
System Scanner SR 3.08

As a workaround for DNS servers that do not need recursive DNS functionality,
it is recommended to disable recursion within the BIND configuration file:

BIND 8, named.conf

options {
        recursion no;

BIND 4, named.boot

options no-recursion

Where disabling recursion is not possible, a temporary workaround exists that
may protect perimeter DNS servers from the remote compromise vulnerability.
Due to the nature and organization of stack variables, exploitation is much
easier if the attack is embedded within TCP DNS traffic. It is unclear at this
time if this attack is possible with UDP traffic on certain architectures. The
UDP protocol is used for most DNS related queries and responses, except large
responses and zone transfers between primary and secondary DNS servers.
Therefore, perimeter DNS servers should be protected by filtering TCP port 53.
This workaround will block the exploit technique demonstrated by X-Force, but
this solution should be examined carefully to determine if it would not affect
normal DNS functionality. This workaround is meant as a temporary solution to
offer some level of protection before a patch can be applied.

ISC has made software patches available. ISC recommends that BIND
installations should be upgraded to BIND version 4.9.11, 8.2.7, 8.3.4 or to
BIND version 9. BIND 9 was not affected by any of the vulnerabilities
described in this advisory. These versions will be available soon at the follow
address: ISC recommends th
all users requesting the security patches should contact for

Additional Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned the
following names to these issues. These are candidates for inclusion in the CVE
list (, which standardizes names for security problems.

CAN-2002-1219 BIND SIG Cached RR Overflow Vulnerability
CAN-2002-1220 BIND OPT DoS
CAN-2002-1221 BIND SIG Expiry Time DoS



These vulnerabilities were discovered and researched by Neel Mehta of the ISS


About Internet Security Systems (ISS) Founded in 1994, Internet Security
Systems (ISS) (Nasdaq: ISSX) is a pioneer and world leader in software
and services that protect critical online resources from an ever-
changing spectrum of threats and misuse. Internet Security Systems is
headquartered in Atlanta, GA, with additional operations throughout the
Americas, Asia, Australia, Europe and the Middle East.

Copyright (c) 2002 Internet Security Systems, Inc. All rights reserved

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