CVE-2009-5155

What it actually does

Misparsing of regex alternatives in parse_reg_exp causes assertion failures leading to application crashes or produces incorrect match results on crafted input.

Why it matters to the business

Services relying on glibc regex processing can experience unexpected crashes or silent incorrect behavior, disrupting operations and potentially requiring restarts or manual intervention across many systems.

How an attack unfolds

An attacker supplies a specially crafted regular expression to any application linked against vulnerable glibc; the misparsed alternatives trigger an assertion or yield wrong results without authentication or user interaction.

How to fix it

Upgrade glibc to version 2.28 or later on all affected systems; rebuild and redeploy any statically linked applications; apply vendor patches for NetApp products once available.

How to confirm the fix worked

Run 'ldd --version' or 'rpm -q glibc' to confirm version >= 2.28; execute regression tests with known problematic regex patterns to verify correct parsing and no assertion failures.

Typical attack path

1. Identify a network-facing or local service that accepts untrusted regex patterns and links to glibc < 2.28
2. Craft a regex containing misparsed alternatives that triggers the assertion or incorrect result
3. Submit the pattern via the service's input channel
4. Observe denial of service through crash or accept incorrect match outcome for further abuse

How to detect it

Search application and system logs for glibc assertion failures mentioning regcomp or posix/regcomp.c; correlate process crashes with receipt of regex-containing requests; review audit logs for unusual regex patterns submitted to services.

What your security team should do

• Prioritize patching glibc on internet-facing systems within the next maintenance window
• Inventory all applications that call regcomp or similar POSIX regex functions
• Monitor for application crashes correlated with regex processing
• Consider temporary input sanitization or regex length limits where upgrades are delayed