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

Advisory record · `GHSA-59f3-vp2f-mp9w`

- **Identifiers:** `GHSA-59f3-vp2f-mp9w` · `CVE-2026-45755` · `PKSA-1jhn-nv8n-vjk2` · `PKSA-n517-312t-6vqg`
- **State:** Confirmed
- **Severity:** CVSS 6.9 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-306](https://cwe.mitre.org/data/definitions/306.html) · [CWE-347](https://cwe.mitre.org/data/definitions/347.html)
- **Tags:** [Authentication bypass](https://agentprime.io/advisories/tag/auth-bypass.md) · [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md)
- **Published:** 28 May 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 28 May 2026, 17:33 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `symfony/mailtrap-mailer` (Packagist): affected `>=7.2.0, <7.4.12 || >=8.0.0, <8.0.12`; fixed in `7.4.12`, `8.0.12`
- `symfony/symfony` (Packagist): affected `>=7.2.0, <7.4.12 || >=8.0.0, <8.0.12`; fixed in `7.4.12`, `8.0.12`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.9 Medium, CVSS 4.0: `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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0027, the 19th percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 20 May 2026, 10:21 UTC: [Published by the maintainers as a GitHub repository advisory](https://github.com/symfony/symfony/security/advisories/GHSA-59f3-vp2f-mp9w)
- 31 Oct 2026, 14:02 UTC: First seen by agentprime
- 31 Oct 2026, 14:02 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-59f3-vp2f-mp9w)

## Sources

- [GitHub Advisory Database: GHSA-59f3-vp2f-mp9w](https://github.com/advisories/GHSA-59f3-vp2f-mp9w)
- [OSV: GHSA-59f3-vp2f-mp9w](https://osv.dev/vulnerability/GHSA-59f3-vp2f-mp9w)
- <https://github.com/symfony/symfony/security/advisories/GHSA-59f3-vp2f-mp9w>
- <https://github.com/symfony/symfony/commit/4e0467e4e182cf2e704a3d9e1bc1a6be65d52ab8>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/mailtrap-mailer/CVE-2026-45755.yaml>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-45755.yaml>
- <https://github.com/symfony/symfony>
- <https://symfony.com/cve-2026-45755>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-59f3-vp2f-mp9w>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-59f3-vp2f-mp9w/>. Everything for agents: <https://agentprime.io/llms.txt>.