GHSA-rrj9-5q2j-4gvr
Fix: symfony/symfony@bdfe9feGHSA-rrj9-5q2j-4gvr is a CWE-347 vulnerability in symfony/mailomat-mailer. O3 Security confirms whether GHSA-rrj9-5q2j-4gvr is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-rrj9-5q2j-4gvr.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
symfony/mailomat-mailer🐘symfony/mailomat-mailer🐘symfony/symfony🐘symfony/symfonyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Description
Symfony\Component\Mailer\Bridge\Mailomat\Webhook\MailomatRequestParser::validateSignature() parses the X-MOM-Webhook-Signature request header as algo=signature and passes the wire-supplied $algo directly to hash_hmac() when verifying the request against the configured webhook secret. The request therefore selects the HMAC primitive used to authenticate it.
PHP's hash_hmac() enforces only that the chosen algorithm is HMAC-compatible. That set still includes primitives with known cryptanalysis (md4, md5, ripemd128, tiger128,3, … — e.g. existential forgery of HMAC-MD4, Contini & Yin, ASIACRYPT 2006). This is the canonical algorithm-confusion shape, analogous to JWT alg=none / alg=HS256 downgrades: any future cryptographic weakness in any HMAC primitive PHP exposes becomes immediately exploitable against a Mailomat webhook receiver, the moment an attacker is in a position to compute a signature for that primitive, without a code change on the Symfony side.
Mailomat's documented webhook security pins SHA-256; the parser did not.
Resolution
MailomatRequestParser::validateSignature() now requires the signature header to be of the form sha256=<hex> and verifies the signature with HMAC-SHA256 keyed by the configured secret using a constant-time comparison. Any other algorithm declared on the wire (including the HMAC primitives PHP would otherwise accept) is rejected.
The patch for this issue is available here for branch 7.4 (and forward-ported to 8.0 and 8.1).
Credits
Symfony would like to thank Omar Alshammari, Essam Alanazi and Alwaleed Alshammari for reporting the issue and Nicolas Grekas for providing the fix.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/mailomat-mailer | ≥ 7.2.0&&< 7.4.13 | 7.4.13 |
| 🐘Packagist | symfony/mailomat-mailer | ≥ 8.0.0&&< 8.0.13 | 8.0.13 |
| 🐘Packagist | symfony/symfony | ≥ 7.2.0&&< 7.4.13 | 7.4.13 |
| 🐘Packagist | symfony/symfony | ≥ 8.0.0&&< 8.0.13 | 8.0.13 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/mailomat-mailer. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update symfony/mailomat-mailer to 7.4.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rrj9-5q2j-4gvr is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-rrj9-5q2j-4gvr is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-rrj9-5q2j-4gvr. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-rrj9-5q2j-4gvr in your dependencies?
O3 detects GHSA-rrj9-5q2j-4gvr across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.