CVE-2026-53550

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.

• CWE-407

• https://github.com/nodeca/js-yaml/security/advisories/GHSA-h67p-54hq-rp68Exploit, Mitigation, Vendor Advisory

Published

Jun 22, 2026

Last Modified

Jul 9, 2026

Status

Analyzed

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