GHSA-2v3c-qxhr-7vpv: symfony/symfony (CVE-2026-109413)

Package	Ecosystem	Affected	Fixed in
symfony/symfony	Packagist	>=2.0.0, <5.4.54 \|\| >=6.0.0, <6.4.45 \|\| >=7.0.0, <7.4.18 \|\| >=8.0.0, <8.1.6	5.4.54, 6.4.45, 7.4.18, 8.1.6
symfony/yaml	Packagist	>=2.0.0, <5.4.54 \|\| >=6.0.0, <6.4.45 \|\| >=7.0.0, <7.4.18 \|\| >=8.0.0, <8.1.6	5.4.54, 6.4.45, 7.4.18, 8.1.6

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Symfony's symfony/symfony and symfony/yaml packages are affected in versions before 5.4.54, from 6.0.0 before 6.4.45, from 7.0.0 before 7.4.18, and from 8.0.0 before 8.1.6. An attacker can supply a YAML document with deeply nested inline collections, which exhausts the stack in the inline lexer and crashes the process or ends the request with a fatal error. Any code parsing untrusted YAML is affected, and no authentication is needed. Upgrade symfony/symfony and symfony/yaml to 5.4.54, 6.4.45, 7.4.18, or 8.1.6 according to your branch.

Written 31 Oct 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
8.7	High	4.0	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	CNA (Checkmarx)

CISA KEV Not listed.
EPSS 0.0040, the 33rd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 13:53 UTC First seen by agentprime
31 Oct 2026, 13:53 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.