Inefficient Algorithmic Complexity Affecting js-yaml package, versions >=5.0.0 <5.2.0
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-JSYAML-17900092
- published9 Jul 2026
- disclosed8 Jul 2026
- creditMazze LeCzzare Frazer
Introduced: 8 Jul 2026
NewCVE-2026-59868 (opens in a new tab)How to fix?
Upgrade js-yaml to version 5.2.0 or higher.
Overview
js-yaml is a human-friendly data serialization language.
Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the merge key (<<) handling during YAML parsing, where each mapping in a chain re-enumerates the keys inherited from the previous mapping. An attacker can exhaust CPU and cause denial of service by supplying a document with N chained merge mappings, which forces roughly O(N²) work for O(N) input. Exploitation requires the application to parse untrusted YAML with merge keys enabled, which is off by default.
Note: This is the js-yaml 5.x instance of the same merge key quadratic-complexity flaw described for the 3.x and 4.x lines in CVE-2026-59869.