Uncontrolled Recursion Affecting symfony/yaml package, versions >=4.1.0, <5.4.54>=6.0.0, <6.4.45>=7.0.0, <7.4.16>=8.0.0, <8.1.6
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PHP-SYMFONYYAML-21203849
- published18 Oct 2026
- disclosed15 Oct 2026
- creditBruno Dias
Introduced: 15 Oct 2026
NewCVE-2026-109413 (opens in a new tab)How to fix?
Upgrade symfony/yaml to version 5.4.54, 6.4.45, 7.4.16, 8.1.6 or higher.
Overview
Affected versions of this package are vulnerable to Uncontrolled Recursion via Parser::lexInlineStructure(), which recurses through lexInlineMapping() and lexInlineSequence() without incrementing the shared nesting-level counter that guards against excessive depth. Because the maxNestingLevel guard is only checked after the lexer returns, a deeply nested inline YAML document (e.g. thousands of nested { or [ characters) exhausts available memory inside the lexer before the guard is ever reached, causing the process to crash. The fix enters and leaves the shared nesting level at the boundary of lexInlineStructure(), so the existing maximum-nesting-depth error is raised consistently for both block and inline structures.