CVE-2026-48747: Symfony Mailomat Mailer signature algorithm downgrade in webhook parser

CVE-2026-48747 · Severity: medium · CVSS 0 · Published 2026-07-14

Symfony is a popular PHP framework used to build web applications. A vulnerability in its Mailomat mailer component could allow an attacker to bypass security checks on incoming webhooks by forcing the system to use weaker, less secure encryption methods. This could potentially allow unauthorized requests to be processed as if they were legitimate communications from the Mailomat service.

Technologies: symfony/symfony (Packagist). Vendors: Packagist, Symfony.

Quick answers

Is CVE-2026-48747 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-48747 being exploited in the wild.
How severe is CVE-2026-48747?
Medium severity, with a CVSS score of 0, published 14 July 2026.
Which products and versions are affected?
symfony/mailomat-mailer (Packagist) ECOSYSTEM:introduced=7.2.0,fixed=7.4.13; symfony/symfony (Packagist) ECOSYSTEM:introduced=7.2.0,fixed=7.4.13.
Is there a fix for CVE-2026-48747?
Yes. symfony/mailomat-mailer (Packagist): upgrade to 7.4.13 or later; symfony/symfony (Packagist): upgrade to 7.4.13 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-48747 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-48747?
Check whether you run symfony/mailomat-mailer (Packagist), symfony/symfony (Packagist) or Symfony Mailomat Mailer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • symfony/mailomat-mailer (Packagist): upgrade to 7.4.13 or later
    composer require symfony/mailomat-mailer:^7.4.13
  • symfony/symfony (Packagist): upgrade to 7.4.13 or later
    composer require symfony/symfony:^7.4.13

Technical details

A signature algorithm downgrade vulnerability exists in the MailomatRequestParser::validateSignature() method within Symfony's Mailomat Mailer bridge. The parser incorrectly extracted the HMAC algorithm directly from the 'X-MOM-Webhook-Signature' request header and passed it to PHP's hash_hmac() function. This allowed a remote attacker to specify weak or broken cryptographic primitives (such as MD4 or MD5) instead of the documented SHA-256 requirement. An attacker could exploit this to forge webhook signatures if they can compute a valid HMAC for a weaker primitive. The issue is resolved in versions 7.4.13 and 8.0.13 by pinning the algorithm to SHA-256 and using constant-time comparison.

Affected products

  • Symfony symfony/mailomat-mailer >= 7.2.0, < 7.4.13; >= 8.0.0-BETA1, < 8.0.13
  • Symfony symfony/symfony >= 7.2.0, < 7.4.13; >= 8.0.0-BETA1, < 8.0.13

Identifiers

  • CVE-2026-48747
  • GHSA-rrj9-5q2j-4gvr

Timeline

  • 2026-05-27: advisory: GitHub Security Advisory published
  • 2026-05-27: patched: Versions 7.4.13 and 8.0.13 released
  • 2026-07-14: disclosed: CVE-2026-48747 published to NVD

References

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