Security researchers have discovered a flaw in Snort, the open-source intrusion detection system that could be used by attackers to run malicious code.

The stack buffer overflow bug is in the Snort (or Sourcefire) DCE/RPC preprocessor, said Neel Mehta, a member of IBM's Internet Security Systems X-Force research team. Mehta discovered the vulnerability, which could result in compromised or hijacked computers.

Danish security company Secunia rated the threat as "highly critical," the second-most-serious ranking in its 1-through-5 scoring system.

Several versions of Snort, which is the foundation of Sourcefire's security appliance line, are at risk, according to other advisories posted by US-CERT and the SANS Institute's Internet Storm Center. The vulnerable versions include Snort 2.6.1, 2.6.1.1, 2.6.1.2, and 2.7.0 Beta 1.

Sourcefire urged users of Snort 2.6.1.x to update to Version 2.6.1.3 "immediately"; if upgrading isn't feasible, the DCE/RPC preprocessor should be disabled. Instructions for disabling the preprocessor are available online.

No working exploit for the vulnerability has been spotted yet, Sourcefire said.