flex: Potential insecure code generation

Background

flex is a programming tool used to generate scanners (programs which recognize lexical patterns in text).

Description

Chris Moore discovered a buffer overflow in a special class of lexicographical scanners generated by flex. Only scanners generated by grammars which use either REJECT, or rules with a “variable trailing context” might be at risk.

Impact

An attacker could feed malicious input to an application making use of an affected scanner and trigger the buffer overflow, potentially resulting in the execution of arbitrary code.

Workaround

Avoid using vulnerable grammar in your flex scanners.

Resolution

All flex users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=sys-devel/flex-2.5.33-r1"