CVE-2026-45755: Symfony Mailtrap mailer bridge signature bypass in MailtrapRequestParser

CVE-2026-45755 · Severity: medium · CVSS 4 · Published 2026-07-14

A vulnerability in the Symfony web framework's Mailtrap integration allows attackers to send fake email event notifications to an application. By bypassing security signature checks, an attacker can forge events such as email bounces, opens, or spam reports. This can lead to corrupted delivery metrics and the incorrect blocking of legitimate email addresses in an organization's mailing lists.

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

Quick answers

Is CVE-2026-45755 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-45755 being exploited in the wild.
How severe is CVE-2026-45755?
Medium severity, with a CVSS score of 4, published 14 July 2026.
Which products and versions are affected?
symfony/mailtrap-mailer (Packagist) ECOSYSTEM:introduced=7.2.0,fixed=7.4.12; symfony/symfony (Packagist) ECOSYSTEM:introduced=7.2.0,fixed=7.4.12; Symfony Mailtrap-Mailer >= 7.2.0, < 7.4.12; >= 8.0.0, < 8.0.12.
Is there a fix for CVE-2026-45755?
Yes. symfony/mailtrap-mailer (Packagist): upgrade to 7.4.12 or later; symfony/symfony (Packagist): upgrade to 7.4.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-45755 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-45755?
Check whether you run symfony/mailtrap-mailer (Packagist), symfony/symfony (Packagist) or Symfony Mailtrap-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/mailtrap-mailer (Packagist): upgrade to 7.4.12 or later
    composer require symfony/mailtrap-mailer:^7.4.12
  • symfony/symfony (Packagist): upgrade to 7.4.12 or later
    composer require symfony/symfony:^7.4.12

Technical details

The MailtrapRequestParser::doParse() method in Symfony's Mailtrap mailer bridge receives a configured webhook secret but fails to utilize it for signature verification. Specifically, the component ignores the X-Mt-Signature HMAC-SHA256 header provided by Mailtrap, processing the POST payload unconditionally. This allows a remote, unauthenticated attacker to submit forged JSON payloads representing delivery, bounce, open, click, or spam events. The vulnerability is classified under CWE-306 (Missing Authentication) and CWE-347 (Improper Verification of Cryptographic Signature). The issue is resolved in versions 7.4.12 and 8.0.12 by enforcing constant-time HMAC verification when a secret is configured.

Affected products

  • Symfony symfony/mailtrap-mailer >= 7.2.0, < 7.4.12; >= 8.0.0, < 8.0.12
  • Symfony symfony/symfony >= 7.2.0, < 7.4.12; >= 8.0.0, < 8.0.12

Identifiers

  • CVE-2026-45755
  • GHSA-59f3-vp2f-mp9w

Timeline

  • 2026-05-20: patched: Fixes released in versions 7.4.12 and 8.0.12
  • 2026-05-20: advisory: GitHub Security Advisory GHSA-59f3-vp2f-mp9w published
  • 2026-07-14: disclosed: CVE-2026-45755 published to NVD

References

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