CVE-2026-45755
Symfony's Mailtrap Mailer Webhook Parser Never Verifies the X-Mt-Signature HMAC — Unauthenticated Webhook Event Injection
Description
### 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 payload, using a constant-time comparison. When no secret is configured the behaviour is unchanged: signature verification remains opt-in, but it is now actually enforced once opted in. The patch for this issue is available [here](https://github.com/symfony/symfony/commit/4e0467e4e182cf2e704a3d9e1bc1a6be65d52ab8) for branch 7.4. ### Credits Symfony would like to thank Himanshu Anand for reporting the issue and Alexandre Daubois providing the fix.
How to fix CVE-2026-45755
To remediate CVE-2026-45755, upgrade the affected package to a fixed version below.
- —upgrade to 7.4.12+dfsg-1 or later
- —upgrade to 7.4.12 or later
- —upgrade to 7.4.12 or later
Is CVE-2026-45755 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-45755.
Affected packages (3)
- from 0, < 7.4.12+dfsg-1
- >= 7.2.0, < 7.4.12
- >= 7.2.0, < 7.4.12
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |