CVE-2026-109413
HighCVSS 8.7Exploitation Probability (EPSS)
Low risk42th percentile - higher than 42% of all known CVEs
Summary
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 being lexed, causing the process to crash or the request to end with a fatal error. Any code parsing untrusted YAML is affected, including #[MapRequestPayload] when the Yaml component is installed and the endpoint does not restrict acceptFormat.
Risk Assessment
A single unauthenticated request with a YAML content type can crash the process or cause a fatal error, leading to denial of service. This affects any application parsing untrusted YAML, including endpoints using #[MapRequestPayload] without restricting acceptFormat.
Recommendation
Update symfony/yaml to version 5.4.54, 6.4.45, 7.4.18, or 8.1.6 (or later). Additionally, restrict accepted formats on endpoints that accept input to exclude untrusted YAML.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

