What’s Vulnerable › Vulnerabilities
CVE-2026-53550: js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases
- Severity: medium (CVSS 5.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-06-22 · updated 2026-10-25
- Weakness: CWE-407
Description
js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0 and 3.15.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0 and 3.15.0.
Affected products
- nodeca js-yaml: before 3.15.0; from 4.0.0 before 4.2.0 — fixed in 3.15.0, 4.2.0
- Npm Js-Yaml: from 4.0.0 before 4.2.0; before 3.15.0 — fixed in 4.2.0, 3.15.0
How to fix
Upgrade to a fixed version: nodeca js-yaml 3.15.0, 4.2.0; Npm Js-Yaml 4.2.0, 3.15.0. Check the vendor advisory for mitigations.
References
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