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Snort RPC Preprocessor Buffer Overflow Vulnerability
04 March 2003
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Snort Vulnerability Advisory [SNORT-2003-001]

Date: 2003-03-03

Affected Snort Versions:

Any version starting with version 1.8 to those before 2003-03-03 1PM/ US/Eastern including 1.9.0 and CVS HEAD (Snort 2.0beta)

Synopsis:

A buffer overflow has been found in the snort RPC normalization routines by ISS X-Force. This can cause snort to execute arbitrary code embedded within sniffed network packets. This preprocessor is enabled by default.

Snort 1.9.1 has been released to resolve this issue. For users using CVS HEAD, a fix has been committed to the source tree.

Mitigation:

If you are in an environment that can not upgrade snort immediately, comment out the line in your snort.conf that begins:

preprocessor rpc_decode

and replace it with

# preprocessor rpc_decode

Details:

When the rpc decoder normalizes fragmented RPC records, it incorrectly checks the lengths of what is being normalized against the current packet size.

The rpc decoder in Snort 1.9.1 and above contains new alert options that can be used to help detect this attack

Option Default State

alert_fragments INACTIVE
alert_large_fragments ACTIVE
alert_incomplete ACTIVE
alert_multiple_requests ACTIVE

The first option will alert on any rpc fragmented record it finds. Large fragments will alert when the reassembled fragment record will exceed the current packet length. The incomplete record will alert when there is a partial record found. The alert_multiple_requests will alert when we find more than one RPC request per packet ( or reassembled packet ).

Download Locations:

Sourcefire has acquired additional bandwidth and hosting to aid users wishing to upgrade their Snort implementation. Binaries are currently not available, this is a source release only at this time. As new binaries become available they will be added to the site.

Source code: http://www.snort.org/dl/snort-1.9.1.tar.gz
GPG Signatures: http://www.snort.org/dl/snort-1.9.1.tar.gz.asc

CVS HEAD (Snort 2.0beta) has been fixed as well.

- --
Martin Roesch - Founder/CTO, Sourcefire Inc. - (410)290-1616
Sourcefire: Snort-based Enterprise Intrusion Detection Infrastructure
roesch@sourcefire.com - http://www.sourcefire.com
Snort: Open Source Network IDS - http://www.snort.org



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