Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · 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 · score source

EPSS

• CVE-2026-109413: 0.40% estimated exploitation activity in the next 30 days; percentile 33.81 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Description `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.

Resolution The inline lexer now enters and leaves the same nesting level as the rest of the parser, so nested inline collections are bounded by `maxNestingLevel`, and the parser raises a `ParseException` beyond it. The patches for this issue are available…

Published by the source

27 Oct 2026, 19:01 UTC

Last modified by the source

27 Oct 2026, 19:15 UTC

Source last checked

28 Oct 2026, 06:30 UTC

1. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-2v3c-qxhr-7vpv

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-2v3c-qxhr-7vpv

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# Patch Next advisory brief: CVE-2026-109413

Advisory: Symfony: Unbounded Recursion in the YAML Inline Lexer Lets a Single Document Crash the Process
IDs: CVE-2026-109413, GHSA-2v3c-qxhr-7vpv
Record: https://patchnext.com/advisories/cve-2026-109413 (revision 2, source checked 28 Oct 2026, 06:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: symfony/symfony 8.1.6, 7.4.18, 6.4.45, 5.4.54; symfony/yaml 8.1.6, 7.4.18, 6.4.45, 5.4.54. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist symfony/symfony: affected >= 2.0.0, < 5.4.54; >= 6.0.0, < 6.4.45; >= 7.0.0, < 7.4.18; >= 8.0.0, < 8.1.6; fixed in 8.1.6, 5.4.54, 7.4.18, 6.4.45
- Packagist symfony/yaml: affected >= 2.0.0, < 5.4.54; >= 6.0.0, < 6.4.45; >= 7.0.0, < 7.4.18; >= 8.0.0, < 8.1.6; fixed in 8.1.6, 5.4.54, 7.4.18, 6.4.45

## Suggested inspection (read-only)
- Packagist symfony/symfony: check the installed version with your package manager.
- Packagist symfony/yaml: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on symfony/symfony, symfony/yaml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2v3c-qxhr-7vpv (GitHub-reviewed advisory GHSA-2v3c-qxhr-7vpv lists affected ranges: Packagist symfony/symfony >=2.0.0 =6.0.0 =7.0.0 =8.0.0 =2.0.0 =6.0.0 =7.0.0 =8.0.0 <8.1.6)
- Verified: https://osv.dev/vulnerability/GHSA-2v3c-qxhr-7vpv (OSV record GHSA-2v3c-qxhr-7vpv lists affected ranges: Packagist symfony/symfony >=2.0.0 =6.0.0 =7.0.0 =8.0.0 =2.0.0 =6.0.0 =7.0.0 =8.0.0 <8.1.6 (fixed))

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