Symfony Yaml: Deeply Nested Inline YAML Crashes the Process

Published as "CVE-2026-109413: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process"

high Symfony Symfony components · Last reviewed Nov 1, 2026

CVE: CVE-2026-109413
GHSA: GHSA-2v3c-qxhr-7vpv
Packagist: PKSA-fyjn-dgwp-4tt3
Reported: Aug 30, 2026

Lets an attacker crash the PHP process with one YAML document in apps that parse untrusted YAML, including some #[MapRequestPayload] endpoints.

Affected and fixed versions

In 2 packages: symfony/symfony and symfony/yaml. 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 – 8.1.5	8.1.6	Supported
7.4.0 – 7.4.17	7.4.18	Supported
6.4.0 – 6.4.44	6.4.45	Supported
5.4.0 – 5.4.53	5.4.54	Supported

Show 16 older branches, no longer supported

8.0.0 – 8.0.x	8.1.6
7.0.0 – 7.0.x	7.4.18
7.1.0 – 7.1.x	7.4.18
7.2.0 – 7.2.x	7.4.18
7.3.0 – 7.3.x	7.4.18
6.0.0 – 6.0.x	6.4.45
6.1.0 – 6.1.x	6.4.45
6.2.0 – 6.2.x	6.4.45
6.3.0 – 6.3.x	6.4.45
2.0.0 – 2.x	5.4.54
3.0.0 – 3.x	5.4.54
4.0.0 – 4.x	5.4.54
5.0.0 – 5.0.x	5.4.54
5.1.0 – 5.1.x	5.4.54
5.2.0 – 5.2.x	5.4.54
5.3.0 – 5.3.x	5.4.54

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/symfony:^8.1.6
composer require symfony/symfony:^7.4.18
composer require symfony/symfony:^6.4.45
composer require symfony/symfony:^5.4.54

What this means

An attacker can crash the PHP process, or end the request with a fatal error, by sending one YAML document made of deeply nested inline lists or maps. The YAML parser's inline reader didn't apply the nesting limit the rest of the parser uses.

Who is affected

Any code that parses YAML from untrusted sources with symfony/yaml, also part of symfony/symfony. The Symfony advisory says that includes endpoints using #[MapRequestPayload] when the Yaml component is installed and the endpoint doesn't restrict acceptFormat. There, a single request with a YAML content type is enough, with no login needed. Apps that only parse their own YAML files, such as config, aren't exposed.

What to do

Update to 5.4.54, 6.4.45, 7.4.18 or 8.1.6. If you're on 8.0, move to 8.1. The fix makes the parser throw a ParseException once a document nests too deep.

Reported and fixed by Nicolas Grekas.

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 Yaml: Deeply Nested Inline YAML Crashes the Process (CVE-2026-109413, GHSA-2v3c-qxhr-7vpv)
Details: https://phpnews.net/security/symfony/ghsa-2v3c-qxhr-7vpv

Affected versions, as Composer constraints:
- symfony/symfony, symfony/yaml: >=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,<5.4.54|>=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,<6.4.45|>=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,<7.4.18|>=8.0.0,<8.1.0|>=8.1.0,<8.1.6

Fixed releases on branches that still get security fixes:
- 8.1.0 – 8.1.5: update to 8.1.6
- 7.4.0 – 7.4.17: update to 7.4.18
- 6.4.0 – 6.4.44: update to 6.4.45
- 5.4.0 – 5.4.53: update to 5.4.54

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-2v3c-qxhr-7vpv 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-2v3c-qxhr-7vpv). 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

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