There is a buffer overflow vulnerability in the RPC preprocessing feature of Snort versions 1.8 through 1.9.0 and 2.0 beta.
Martin Roesch, the primary Snort developer, described the vulnerability by saying:
When the RPC decoder normalizes fragmented RPC records, it incorrectly checks the lengths of what is being normalized against the current packet size, leading to an overflow condition. The RPC preprocessor is enabled by default.
A remote attacker can execute arbitrary code as the user running the Snort process, usually root. The attacker does not need to send packets directly to the Snort sensor. It is sufficient to send packets to any of the hosts on the network monitored by Snort.
Upgrade to Snort version 1.9.1
Disable the rpc_decode preprocessor
Guardian Digital Inc.
Apple Computer Inc.
Red Hat Inc.
Sun Microsystems Inc.
The SCO Group (SCO Linux)
The SCO Group (SCO UnixWare)
Wind River Systems Inc.
Thanks to ISS X-Force for discovering this vulnerability, and to Martin Roesch for his assistance in developing this document.