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AUSCERT External Security Bulletin Redistribution
ESB-2000.322 -- FreeBSD-SA-00:61
tcpdump contains remote vulnerabilities
31 October 2000
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AusCERT Security Bulletin Summary
---------------------------------
Product: tcpdump
Vendor: FreeBSD
Operating System: FreeBSD
BSD
Impact: Execute Arbitrary Code/Commands
Access Required: Remote
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FreeBSD-SA-00:61 Security Advisory
FreeBSD, Inc.
Topic: tcpdump contains remote vulnerabilities
Category: core
Module: tcpdump
Announced: 2000-10-31
Credits: Discovered during internal auditing.
Affects: All releases of FreeBSD 3.x, 4.x prior to 4.2
FreeBSD 3.5.1-STABLE and 4.1.1-STABLE prior to the
correction date
Corrected: 2000-10-04 (FreeBSD 4.1.1-STABLE)
2000-10-05 (FreeBSD 3.5.1-STABLE)
Vendor status: Patch released
FreeBSD only: NO
I. Background
tcpdump is a tool for monitoring network activity.
II. Problem Description
Several overflowable buffers were discovered in the version of tcpdump
included in FreeBSD, during internal source code auditing. Some
simply allow the remote attacker to crash the local tcpdump process,
but there is a more serious vulnerability in the decoding of AFS ACL
packets in the more recent version of tcpdump (tcpdump 3.5) included
in FreeBSD 4.0-RELEASE, 4.1-RELEASE and 4.1.1-RELEASE, which may allow
a remote attacker to execute arbitrary code on the local system
(usually root, since root privileges are required to run tcpdump).
The former issue may be a problem for systems using tcpdump as a form
of intrusion detection system, i.e. to monitor suspicious network
activity: after the attacker crashes any listening tcpdump processes
their subsequent activities will not be observed.
All released versions of FreeBSD prior to the correction date
including 3.5.1-RELEASE, 4.0-RELEASE, 4.1-RELEASE and 4.1.1-RELEASE
are vulnerable to the "remote crash" problems, and FreeBSD
4.0-RELEASE, 4.1-RELEASE and 4.1.1-RELEASE are also vulnerable to the
"remote execution" vulnerability. Both problems were corrected in
4.1.1-STABLE prior to the release of FreeBSD 4.2-RELEASE.
III. Impact
Remote users can cause the local tcpdump process to crash, and (under
FreeBSD 4.0-RELEASE, 4.1-RELEASE, 4.1.1-RELEASE and 4.1.1-STABLE prior
to the correction date) may be able to cause arbitrary code to be
executed as the user running tcpdump, usually root.
IV. Workaround
Do not use vulnerable versions of tcpdump in network environments
which may contain packets from untrusted sources.
V. Solution
One of the following:
1) Upgrade your vulnerable FreeBSD system to 4.1.1-STABLE or
3.5.1-STABLE after the respective correction dates.
2a) FreeBSD 3.x systems prior to the correction date
Download the patch and the detached PGP signature from the following
locations, and verify the signature using your PGP utility.
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:61/tcpdump-3.x.patch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:61/tcpdump-3.x.patch.asc
# cd /usr/src/contrib/tcpdump
# patch -p < /path/to/patch
# cd /usr/src/usr.sbin/tcpdump
# make depend && make all install
2b) FreeBSD 4.x systems prior to the correction date
Download the patch and the detached PGP signature from the following
locations, and verify the signature using your PGP utility.
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:61/tcpdump-4.x.patch
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:61/tcpdump-4.x.patch.asc
# cd /usr/src/contrib/tcpdump
# patch -p < /path/to/patch
# cd /usr/src/usr.sbin/tcpdump
# make depend && make all install
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