CVE-2026-48747 Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade

What is CVE-2026-48747?

CVE-2026-48747 is a medium-severity vulnerability in Sensiolabs Symfony, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 7.4.13 and 8.0.13, MailomatRequestParser::validateSignature() parsed X-MOM-Webhook-Signature as algo=signature and passed the request-selected algorithm to hash_hmac(), allowing a signature algorithm downgrade instead of enforcing Mailomat's documented SHA-256 webhook signature. This issue is fixed in versions 7.4.13 and 8.0.13.

Weakness: CWE-757, CWE-347

Which versions are affected by CVE-2026-48747?

8 open source packages ship an affected version, including symfony/mailomat-mailer and symfony/symfony. It affects 1 product.

Products include Sensiolabs Symfony.

How do I fix CVE-2026-48747?

Upgrade symfony/mailomat-mailer to a fixed version for your release line: 7.4.13 or 8.0.13.

Is CVE-2026-48747 being exploited?

There is no known exploitation of CVE-2026-48747 in the wild and no public exploit code.

Other vulnerabilities in Sensiolabs Symfony

• CVE-2019-11325 Improper Input Validation in Symfony Critical 9.8
• CVE-2017-11365 Symfony Incorrect Access Control Critical 9.8
• CVE-2019-10913 Invalid HTTP method overrides allow possible XSS or other attacks in Symfony Critical 9.8
• CVE-2018-11407 Symfony Authentication Bypass Critical 9.8
• CVE-2016-2403 Symfony Authentication Bypass Critical 9.8

All Sensiolabs Symfony vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-48747, GHSA-rrj9-5q2j-4gvr, UBUNTU-CVE-2026-48747.