[UNIX] FreeBSD Kadmind Remote Heap Buffer Overflow
From: SecuriTeam (support_at_securiteam.com)
Date: 05/06/04
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To: list@securiteam.com Date: 6 May 2004 18:30:29 +0200
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FreeBSD Kadmind Remote Heap Buffer Overflow
------------------------------------------------------------------------
SUMMARY
A remotely exploitable heap overflow was found in FreeBSD's kadmind.
Heimdal implements the Kerberos 5 authentication protocol. The kadmind
provides the administrative interface to the Kerberos Key Distribution
Center (KDC). In some configurations, Kerberos 4 support is present.
DETAILS
Vulnerable Systems:
* FreeBSD version 4 built with either Kerberos 4 or 5
* FreeBSD version 5 prior to 5.1 built with either Kerberos 4 or 5
Immune Systems:
* FreeBSD 4 STABLE (dated after the correction date)
* FreeBSD RELENG_4_8 and RELENG_4_9 (dated after the correction date)
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0434>
CAN-2004-0434
An input validation error was discovered in the k5admind code that handles
the framing of Kerberos 4 compatibility administration requests. The code
assumed that the length given in the framing was always two or more bytes.
Smaller lengths will cause k5admind to read an arbitrary amount of data
into a minimally sized buffer on the heap.
Note that this code is not present unless k5admind has been compiled with
Kerberos 4 support. This will occur if a FreeBSD system is compiled with
both of WITH_KERBEROS4 and WITH_KERBEROS5 build flags. These flags are
never simultaneously set during the FreeBSD binary release process;
consequently, binary installs of FreeBSD (even with Kerberos support
installed) are not affected.
Impact
A remote attacker can send a specially formatted message to the k5admin
daemon that will cause it to either crash or end in arbitrary code
execution.
Workaround
Disable the Kerberos 4 support in k5admind by running it with the
`--no-kerberos4' option.
Solution
Perform one of the following:
1) Upgrade your vulnerable system to 4-STABLE; or to the RELENG_4_9 or
RELENG_4_8 security branch dated after the correction date.
2) To patch your present system:
The following patches have been verified to apply to FreeBSD 4.8 and
4.9.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:09/kadmind.patch
# fetch
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:09/kadmind.patch.asc
b) Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/kerberos5/tools
# make obj && make depend && make
# cd /usr/src/kerberos5/lib
# make obj && make depend && make
# cd /usr/src/kerberos5/libexec/k5admind
# make obj && make depend && make all install
ADDITIONAL INFORMATION
The information has been provided by <mailto:demidov@gleg.net> Evgeny
Demidov.
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