---
title: "CVE-2026-109413: Symfony YAML - Denial of Service"
description: "Symfony YAML < 5.4.54, 6.4.45, 7.4.18, and 8.1.6 contains a denial of service caused by unbounded recursion in lexInlineStructure() when parsing deeply nested inline collections, letting unauthenticated attackers crash the process via crafted YAML payloads, exploit requires sending a YAML content type request."
url: https://panop.io/threat-heartbeat/CVE-2026-109413/
---

# CVE-2026-109413 Symfony YAML - Denial of Service

Symfony YAML < 5.4.54, 6.4.45, 7.4.18, and 8.1.6 contains a denial of service caused by unbounded recursion in lexInlineStructure() when parsing deeply nested inline collections, letting unauthenticated attackers crash the process via crafted YAML payloads, exploit requires sending a YAML content type request.

CVSS base score 8.7 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-109413)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Published

15 October 2026

Updated

15 October 2026

Weakness

[CWE-674](https://cwe.mitre.org/data/definitions/674.html)

## Vendor fix

Upgrade to versions 5.4.54, 6.4.45, 7.4.18, 8.1.6 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-109413](https://nvd.nist.gov/vuln/detail/CVE-2026-109413)
- [https://symfony.com/blog/cve-2026-109413-unbounded-recursion-in-the-yaml-inline-lexer-lets-a-single-document-crash-the-process](https://symfony.com/blog/cve-2026-109413-unbounded-recursion-in-the-yaml-inline-lexer-lets-a-single-document-crash-the-process)
- [https://github.com/symfony/symfony/pull/65688](https://github.com/symfony/symfony/pull/65688)
- [https://github.com/symfony/symfony/security/advisories/GHSA-2v3c-qxhr-7vpv](https://github.com/symfony/symfony/security/advisories/GHSA-2v3c-qxhr-7vpv)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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