UnratedPackagistPublished
Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade
CVE-2026-48747 · GHSA-rrj9-5q2j-4gvr
- Affected
- Packagist symfony/mailomat-mailer >= 7.2.0, < 7.4.13; >= 8.0.0, < 8.0.13
- Fixed in
- 8.0.137.4.13· Vendor fix available
- Issue
- 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 hashhmac() when verifying the request against the configured webhook secret. The request therefore selects the HMAC primitive used to authenticate it. PHP's hashhmac() 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…
Recommended action: Upgrade to 8.0.13 or 7.4.13 by release line, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.