Description
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.
Published: 2026-10-15
Score: 8.7 High
EPSS: n/a
KEV: No
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Remediation

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History

Thu, 15 Oct 2026 15:45:00 +0000

Type Values Removed Values Added
Description 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 prior to v5.4.54, v6.0.0-BETA1 prior to v6.4.45, v7.0.0-BETA1 prior to v7.4.18, and v8.0.0-BETA1 prior to v8.1.6. 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.

Thu, 15 Oct 2026 15:00:00 +0000

Type Values Removed Values Added
Description 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 prior to v5.4.54, v6.0.0-BETA1 prior to v6.4.45, v7.0.0-BETA1 prior to v7.4.18, and v8.0.0-BETA1 prior to v8.1.6.
Title Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process
First Time appeared Sensiolabs
Sensiolabs symfony
Weaknesses CWE-674
CPEs cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*
Vendors & Products Sensiolabs
Sensiolabs symfony
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Subscriptions

Sensiolabs Symfony
cve-icon MITRE

Status: PUBLISHED

Assigner: Checkmarx

Published:

Updated: 2026-10-15T15:29:00.531Z

Reserved: 2026-10-12T15:28:55.069Z

Link: CVE-2026-109413

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-15T15:17:24.993

Modified: 2026-10-15T16:17:43.703

Link: CVE-2026-109413

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses