EUVD-2026-44361
GHSA-59f3-vp2f-mp9w
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from Vendor (https://github.com/symfony/symfony) · only source for this CVE.
CVSS VectorVendor: https://github.com/symfony/symfony
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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3DescriptionCVE.org
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 for branch 7.4.
Credits
Symfony would like to thank Himanshu Anand for reporting the issue and Alexandre Daubois providing the fix.
AnalysisAI
Unauthenticated webhook event injection in Symfony's Mailtrap Mailer bridge (symfony/mailtrap-mailer) allows any remote attacker who knows the webhook endpoint URL to POST arbitrary forged event payloads - delivery, bounce, open, click, or spam - regardless of whether a signing secret is configured. The root cause is that MailtrapRequestParser::doParse() accepts the configured secret as a parameter but never reads it, leaving the X-Mt-Signature HMAC header completely unchecked. Successful exploitation enables suppression-list poisoning, delivery-metrics fraud, and manipulation of application logic that reacts to email events. No public exploit code or active exploitation (CISA KEV) has been identified at time of analysis; the vendor patch is available in versions 7.4.12 and 8.0.12.
Technical ContextAI
The affected code resides in MailtrapRequestParser::doParse() within Symfony's Mailer component bridge for Mailtrap (pkg:composer/symfony/mailtrap-mailer and pkg:composer/symfony/symfony). Mailtrap's webhook mechanism is designed around HMAC-SHA256 request signing: for each outbound POST, Mailtrap computes an HMAC of the raw request body using the configured shared secret and includes it in the X-Mt-Signature header. The parser's method signature accepts the secret via a #[\SensitiveParameter]-annotated parameter, indicating the developer intended it to be used for verification, but the implementation never references the parameter and returns the decoded payload unconditionally. This maps directly to CWE-306 (Missing Authentication for Critical Function) - a critical security gate (signature verification) is simply absent despite being structurally expected. The fix introduced in commit 4e0467e uses hash_equals() for constant-time HMAC-SHA256 comparison, correctly guarding against both missing-signature and wrong-signature cases, and also addresses the implicit timing-oracle risk that a naive string comparison would have introduced.
RemediationAI
Upgrade symfony/mailtrap-mailer (or symfony/symfony if using the monorepo) to version 7.4.12 or 8.0.12 - these are the vendor-released patched versions confirmed by the GHSA advisory at https://github.com/symfony/symfony/security/advisories/GHSA-59f3-vp2f-mp9w. The specific upstream fix is commit 4e0467e4e182cf2e704a3d9e1bc1a6be65d52ab8 on the 7.4 branch. For teams unable to upgrade immediately, a targeted workaround is to place signature verification at the application layer or reverse proxy before the Symfony webhook controller is reached: add a middleware or firewall rule that validates the X-Mt-Signature HMAC-SHA256 header against the raw request body using the configured secret, rejecting any request where the header is absent or mismatched. Note that this compensating control requires careful implementation to avoid timing-oracle vulnerabilities - use a constant-time comparison function. A network-level control (restricting the webhook endpoint to Mailtrap's published IP ranges) is also a viable layered mitigation but introduces operational dependency on Mailtrap's IP range stability and does not address the code defect itself.
Same technique Authentication Bypass
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External POC / Exploit Code
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