CVE-2026-59868: js-yaml: YAML merge-key chains can force quadratic CPU consumption

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-07-08 · updated 2026-10-25
Weakness: CWE-407

Description

js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each mapping merges the previous one. This issue is fixed in version 5.2.0.

Affected products

nodeca js-yaml: from 5.0.0 before 5.2.0 — fixed in 5.2.0

How to fix

Upgrade to a fixed version: nodeca js-yaml 5.2.0. Check the vendor advisory for mitigations.

References

https://github.com/nodeca/js-yaml/commit/3105455b81dee69e0fd36e09ac0b2ccfdb54adc1
https://github.com/nodeca/js-yaml/releases/tag/5.2.0
https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv
https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv

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