Symfony Mime: Header Injection Through Mime Parameter Names

Published as "CVE-2026-45070: Email Header Injection via Non-Token Characters in Mime Parameter Names"

medium Symfony Symfony components · Last reviewed Oct 31, 2026

CVE: CVE-2026-45070
GHSA: GHSA-vqc8-7275-q272
Packagist: PKSA-wtxr-p26d-nn42
Reported: Oct 28, 2026

Lets an attacker add extra email headers in apps that build a Content-Type or Content-Disposition parameter name from user input.

Affected and fixed versions

In 2 packages: symfony/mime and symfony/symfony. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
8.1.0 – 8.1.9	8.1.10	Supported
7.4.0 – 7.4.21	7.4.22	Supported
6.4.0 – 6.4.48	6.4.49	Supported
5.4.0 – 5.4.54	5.4.55	Supported

Show 16 older branches, no longer supported

8.0.0 – 8.0.x	8.1.10
7.0.0 – 7.0.x	7.4.22
7.1.0 – 7.1.x	7.4.22
7.2.0 – 7.2.x	7.4.22
7.3.0 – 7.3.x	7.4.22
6.0.0 – 6.0.x	6.4.49
6.1.0 – 6.1.x	6.4.49
6.2.0 – 6.2.x	6.4.49
6.3.0 – 6.3.x	6.4.49
2.0.0 – 2.x	5.4.55
3.0.0 – 3.x	5.4.55
4.0.0 – 4.x	5.4.55
5.0.0 – 5.0.x	5.4.55
5.1.0 – 5.1.x	5.4.55
5.2.0 – 5.2.x	5.4.55
5.3.0 – 5.3.x	5.4.55

Upgrade

Run the line for the branch you are on. 1 other package listed above is affected too; update it the same way.

composer require symfony/mime:^8.1.10
composer require symfony/mime:^7.4.22
composer require symfony/mime:^6.4.49
composer require symfony/mime:^5.4.55

What this means

An attacker who controls the name of a parameter in a structured email header, such as Content-Disposition, can end that header early and add headers of their own to the message. Symfony checked parameter values but wrote parameter names out exactly as given.

Who is affected

Apps that send mail with the Mime component (symfony/mime, also part of symfony/symfony) and let user input decide a parameter name in headers like Content-Type or Content-Disposition. Parameter values were already checked and encoded, so apps that only put user input in values, like an attachment's file name, aren't exposed.

What to do

Update to 5.4.55, 6.4.49, 7.4.22 or 8.1.10. Symfony 8.0 no longer gets fixes, so 8.0 users need 8.1.10.

The Symfony advisory first listed 5.4.52, 6.4.40, 7.4.12 and 8.0.12 as fixed. The fix never made it into those releases, so if you updated to one of them, you're still affected. The fix rejects parameter names with characters the email standards don't allow.

Reported by Fabian Fleischer.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Symfony Mime: Header Injection Through Mime Parameter Names (CVE-2026-45070, GHSA-vqc8-7275-q272)
Details: https://phpnews.net/security/symfony/ghsa-vqc8-7275-q272

Affected versions, as Composer constraints:
- symfony/mime, symfony/symfony: >=2.0.0,<3.0.0|>=3.0.0,<4.0.0|>=4.0.0,<5.0.0|>=5.0.0,<5.1.0|>=5.1.0,<5.2.0|>=5.2.0,<5.3.0|>=5.3.0,<5.4.0|>=5.4.0,<5.4.55|>=6.0.0,<6.1.0|>=6.1.0,<6.2.0|>=6.2.0,<6.3.0|>=6.3.0,<6.4.0|>=6.4.0,<6.4.49|>=7.0.0,<7.1.0|>=7.1.0,<7.2.0|>=7.2.0,<7.3.0|>=7.3.0,<7.4.0|>=7.4.0,<7.4.22|>=8.0.0,<8.1.0|>=8.1.0,<8.1.10

Fixed releases on branches that still get security fixes:
- 8.1.0 – 8.1.9: update to 8.1.10
- 7.4.0 – 7.4.21: update to 7.4.22
- 6.4.0 – 6.4.48: update to 6.4.49
- 5.4.0 – 5.4.54: update to 5.4.55

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/symfony/ghsa-vqc8-7275-q272 and check whether the project meets the conditions it describes (a feature in use, a config value, a driver) (if that page won't load, use https://github.com/advisories/GHSA-vqc8-7275-q272). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

← All Symfony advisories