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Medium, CVSS 6.6

Symfony's Mailtrap Mailer Webhook Parser Never Verifies the X-Mt-Signature HMAC — Unauthenticated Webhook Event Injection

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

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (symfony/symfony 8.0.12, 7.4.12; symfony/mailtrap-mailer 8.0.12, 7.4.12), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Packagist symfony/symfony

    Affected
    >= 7.2.0, < 7.4.12>= 8.0.0, < 8.0.12
    Fixed in
    8.0.12, 7.4.12

  • Packagist symfony/mailtrap-mailer

    Affected
    >= 7.2.0, < 7.4.12>= 8.0.0, < 8.0.12
    Fixed in
    8.0.12, 7.4.12

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.6 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U · score source
EPSS
  • CVE-2026-45755: 0.27% estimated exploitation activity in the next 30 days; percentile 18.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Description The Mailtrap mailer bridge ships a webhook request parser used to authenticate and decode the event callbacks Mailtrap POSTs to an application's webhook endpoint. Its doParse(Request $request, #[\SensitiveParameter] string $secret) method receives the configured webhook secret but never reads it; it decodes and returns the payload unconditionally, ignoring the X-Mt-Signature HMAC header Mailtrap sends with each request. As a result, an application that wires up the Mailtrap webhook endpoint accepts any POST to that URL, even when a signing secret is configured (the recommended setup). An attacker who knows the endpoint exists can submit forged event payloads, fake delivery / bounce / open / click / spam events, leading to suppression-list corruption, delivery-metrics fraud, etc. Resolution MailtrapRequestParser::doParse() now requires and verifies the X-Mt-Signature header, an HMAC-SHA256 of the raw request body keyed with the configured secret, before decoding the…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-59f3-vp2f-mp9w

Agent brief

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# Patch Next advisory brief: CVE-2026-45755

Advisory: Symfony's Mailtrap Mailer Webhook Parser Never Verifies the X-Mt-Signature HMAC — Unauthenticated Webhook Event Injection
IDs: CVE-2026-45755, GHSA-59f3-vp2f-mp9w
Record: https://patchnext.com/advisories/cve-2026-45755 (revision 1, source checked 26 Oct 2026, 14:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/symfony 8.0.12, 7.4.12; symfony/mailtrap-mailer 8.0.12, 7.4.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/symfony: affected >= 7.2.0, < 7.4.12; >= 8.0.0, < 8.0.12; fixed in 8.0.12, 7.4.12
- Packagist symfony/mailtrap-mailer: affected >= 7.2.0, < 7.4.12; >= 8.0.0, < 8.0.12; fixed in 8.0.12, 7.4.12

## Suggested inspection (read-only)
- Packagist symfony/symfony: check the installed version with your package manager.
- Packagist symfony/mailtrap-mailer: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/symfony, symfony/mailtrap-mailer.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-59f3-vp2f-mp9w (GitHub-reviewed advisory GHSA-59f3-vp2f-mp9w lists affected ranges: Packagist symfony/mailtrap-mailer >=7.2.0 =8.0.0 =7.2.0 =8.0.0 <8.0.12)

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