In Symfony YAML prior to versions 5.4.54, 6.4.45, 7.4.18, and 8.1.6, Yaml\Parser::lexInlineStructure() recursed through lexInlineMapping() and lexInlineSequence() for every { and [ of an inline collection, without entering the nesting le…

Overview

In Symfony YAML prior to versions 5.4.54, 6.4.45, 7.4.18, and 8.1.6, 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.

This issue affects symfony/yaml through v5.4.53, v6.0.0-BETA1 through v6.4.44, v7.0.0-BETA1 through v7.4.17, and v8.0.0-BETA1 through v8.1.5.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Package advisory (CVE-2026-109413)

Affected packages:

• symfony/symfony >= 2.0.0, < 5.4.54
• symfony/symfony >= 6.0.0, < 6.4.45
• symfony/symfony >= 7.0.0, < 7.4.18
• symfony/symfony >= 8.0.0, < 8.1.6
• symfony/yaml >= 2.0.0, < 5.4.54
• symfony/yaml >= 6.0.0, < 6.4.45
• symfony/yaml >= 7.0.0, < 7.4.18
• symfony/yaml >= 8.0.0, < 8.1.6

Patched in:

• symfony/symfony 5.4.54
• symfony/symfony 6.4.45
• symfony/symfony 7.4.18
• symfony/symfony 8.1.6
• symfony/yaml 5.4.54
• symfony/yaml 6.4.45
• symfony/yaml 7.4.18
• symfony/yaml 8.1.6

Source: https://github.com/advisories/GHSA-2v3c-qxhr-7vpv