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GHSA-2v3c-qxhr-7vpvhigh8.7

Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process

Impact

Yaml\Parser::lexInlineStructure() recursed through lexInlineMapping() and lexInlineSequence() for every { and [ of an inline collection, without entering the nesting level that the rest of the parser bounds with maxNestingLevel. A document made of deeply nested inline collections, such as [[[[...]]]], exhausted the stack while it was being lexed: depending on the PHP version and its stack settings, the process crashed or the request ended with a fatal error.

Source excerpt · OSV

Affected packages

Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.

symfony/symfony Packagist
Affected rangeRecorded fix
From 2.0.0 before 5.4.54Ecosystem versions5.4.54
From 6.0.0 before 6.4.45Ecosystem versions6.4.45
From 7.0.0 before 7.4.18Ecosystem versions7.4.18
From 8.0.0 before 8.1.6Ecosystem versions8.1.6

Version evidence: OSV · GHSA-2v3c-qxhr-7vpv

View original version evidence (861 explicit versions)
symfony/yaml Packagist
Affected rangeRecorded fix
From 2.0.0 before 5.4.54Ecosystem versions5.4.54
From 6.0.0 before 6.4.45Ecosystem versions6.4.45
From 7.0.0 before 7.4.18Ecosystem versions7.4.18
From 8.0.0 before 8.1.6Ecosystem versions8.1.6

Version evidence: OSV · GHSA-2v3c-qxhr-7vpv

View original version evidence (673 explicit versions)

Original source description

Description

Yaml\Parser::lexInlineStructure() recursed through lexInlineMapping() and lexInlineSequence() for every { and [ of an inline collection, without entering the nesting level that the rest of the parser bounds with maxNestingLevel. A document made of deeply nested inline collections, such as [[[[...]]]], exhausted the stack while it was being lexed: depending on the PHP version and its stack settings, the process crashed or the request ended with a fatal error.

Any code parsing untrusted YAML is affected. That includes #[MapRequestPayload] when the Yaml component is installed and the endpoint does not restrict acceptFormat: a single unauthenticated request with a YAML content type is enough.

Resolution

The inline lexer now enters and leaves the same nesting level as the rest of the parser, so nested inline collections are bounded by maxNestingLevel, and the parser raises a ParseException beyond it.

The patches for this issue are available here for branch 5.4 (and forward-ported to 6.4, 7.4, 8.1 and 8.2).

Credits

We would like to thank Nicolas Grekas for reporting the issue and providing the fix.

References

References