js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0, 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.
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History
Mon, 22 Jun 2026 15:45:00 +0000
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| Description | js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0, 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. | |
| Title | js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases | |
| Weaknesses | CWE-407 | |
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MITRE
Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-06-22T14:59:14.906Z
Reserved: 2026-06-09T18:13:07.263Z
Link: CVE-2026-53550
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
Updated: 2026-06-22T16:30:08Z