---
id: CVE-2026-109413
title: "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…"
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 le…"
severity: high
cvss: 8.7
cvssVector: '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'
cwe:
  - CWE-674
vendor: sensiolabs
product: symfony/yaml
affected:
  - symfony/yaml < v5.4.54
  - symfony/yaml >= v6.0.0-BETA1 < v6.4.45
  - symfony/yaml >= v7.0.0-BETA1 < v7.4.18
  - symfony/yaml >= v8.0.0-BETA1 < v8.1.6
published: '2026-10-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T19:17:20.987'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-109413'
references:
  - url: 'https://github.com/symfony/symfony/pull/65688'
    label: 596c5446-0ce5-4ba2-aa66-48b3b757a647
  - url: 'https://github.com/symfony/symfony/security/advisories/GHSA-2v3c-qxhr-7vpv'
    label: 596c5446-0ce5-4ba2-aa66-48b3b757a647
  - url: >-
      https://symfony.com/blog/cve-2026-109413-unbounded-recursion-in-the-yaml-inline-lexer-lets-a-single-document-crash-the-process
    label: 596c5446-0ce5-4ba2-aa66-48b3b757a647
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-15T18:06:37.552332Z'
cvssSource: cna
ingestedAt: '2026-10-15T15:09:08.424Z'
---

## 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.