{"id":"CVE-2026-53550","aliases":["GHSA-h67p-54hq-rp68"],"url":"https://o3.security/vulnerability/CVE-2026-53550","summary":"js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases","details":"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.","published":"2026-06-22T14:59:14.906Z","modified":"2026-09-05T09:55:55.981089199Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00386,"percentile":0.32085,"asOf":"2026-09-13"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"js-yaml","fixedVersion":"4.2.0"},{"ecosystem":"npm","name":"js-yaml","fixedVersion":"3.15.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/53xxx/CVE-2026-53550.json"},{"type":"ADVISORY","url":"https://github.com/nodeca/js-yaml/security/advisories/GHSA-h67p-54hq-rp68"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53550"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-05T09:55:55.981089199Z"}}