In Symfony YAML prior to versions 5.4.54, 6.4.45, 7.4.18, and 8.1.6, Yaml\Parser::lexInlineStructure() recursed
Affects symfonySource GCVE Database
Not known to be exploited · CVSS 8.7 High.
Data as of 29 Oct 2026, 00:13 UTC
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 15 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10symfonypkg:deb/ubuntu/symfony?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSsymfonypkg:deb/ubuntu/symfony?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu Pro 24.04 LTSsymfonypkg:deb/ubuntu/symfony?arch=source&distro=esm-apps/nobleOther threats | Affected
| Fixed in– |
Ubuntu Pro 22.04 LTSsymfonypkg:deb/ubuntu/symfony?arch=source&distro=esm-apps/jammyOther threats | Affected
| Fixed in– |
Ubuntu Pro 20.04 LTSsymfonypkg:deb/ubuntu/symfony?arch=source&distro=esm-apps/focalOther threats | Affected
| Fixed in– |
Ubuntu Pro 18.04 LTSsymfonypkg:deb/ubuntu/symfony?arch=source&distro=esm-apps/bionicOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade Symfony YAML to versions 5.4.54, 6.4.45, 7.4.18, or 8.1.6 or later where this issue is fixed. Restrict endpoints that accept YAML input by limiting acceptFormat or applying input validation to prevent deeply nested inline collections. Since a fix is available in the stated versions, applying the official patch is the recommended remediation.
Description
Symfony YAML versions prior to 5.4.54, 6.4.45, 7.4.18, and 8.1.6 contain a vulnerability in Yaml\Parser::lexInlineStructure() where deeply nested inline collections can cause stack exhaustion. This occurs because the parser recurses through inline mappings and sequences without respecting the maxNestingLevel limit, leading to crashes or fatal errors when processing untrusted YAML input. The vulnerability affects any code parsing untrusted YAML, including endpoints using #[MapRequestPayload] without restricting acceptFormat. A single unauthenticated YAML request can trigger this issue.
References
- ubuntu.com/security/CVE-2026-109413 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-109413 (opens in a new tab)
- github.com/symfony/symfony/pull/65688 (opens in a new tab)
- github.com/symfony/symfony/security/advisories/GHSA-2v3c-qxhr-7vpv (opens in a new tab)
- symfony.com/blog/cve-2026-109413-unbounded-recursion-in-the-yaml-inline-lexer-lets-a-single-document-crash-the-process (opens in a new tab)