# Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade

Advisory record · `GHSA-rrj9-5q2j-4gvr`

- **Identifiers:** `GHSA-rrj9-5q2j-4gvr` · `CVE-2026-48747` · `PKSA-9y9v-rcsm-h82j` · `PKSA-v1cq-8qyb-2p5n`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-347](https://cwe.mitre.org/data/definitions/347.html) · [CWE-757](https://cwe.mitre.org/data/definitions/757.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md) · [CWE-757](https://agentprime.io/advisories/tag/cwe-757.md)
- **Published:** 15 Jun 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 15 Jun 2026, 17:32 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `symfony/mailomat-mailer` (Packagist): affected `>=7.2.0, <7.4.13 || >=8.0.0, <8.0.13`; fixed in `7.4.13`, `8.0.13`
- `symfony/symfony` (Packagist): affected `>=7.2.0, <7.4.13 || >=8.0.0, <8.0.13`; fixed in `7.4.13`, `8.0.13`

## 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

- 6.3 Medium, CVSS 4.0: `CVSS:4.0/AV:N/AC:H/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:** 0.0025, the 16th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:00 UTC: First seen by agentprime
- 31 Oct 2026, 14:00 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-rrj9-5q2j-4gvr)

## Sources

- [GitHub Advisory Database: GHSA-rrj9-5q2j-4gvr](https://github.com/advisories/GHSA-rrj9-5q2j-4gvr)
- [OSV: GHSA-rrj9-5q2j-4gvr](https://osv.dev/vulnerability/GHSA-rrj9-5q2j-4gvr)
- <https://github.com/symfony/symfony/security/advisories/GHSA-rrj9-5q2j-4gvr>
- <https://github.com/symfony/symfony/commit/bdfe9fe0d94d33dfaca0bc2fe0b00b54767b0c88>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/mailomat-mailer/CVE-2026-48747.yaml>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-48747.yaml>
- <https://github.com/symfony/symfony>
- <https://symfony.com/cve-2026-48747>

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-rrj9-5q2j-4gvr>, 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-rrj9-5q2j-4gvr/>. Everything for agents: <https://agentprime.io/llms.txt>.