Inefficient Algorithmic Complexity Affecting js-yaml package, versions >=5.0.0 <5.2.1
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-17900063
- published9 Jul 2026
- disclosed8 Jul 2026
- creditUsama Arshad
Introduced: 8 Jul 2026
NewCVE-2026-59870 (opens in a new tab)How to fix?
Upgrade js-yaml to version 5.2.1 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 omapTag.addItem() function of src/tag/sequence/omap.ts, which performs a linear scan for duplicate keys on every insertion into an ordered map. An attacker can block the Node.js event loop and cause denial of service by supplying an !!omap value with many entries, around 50,000 in a roughly 2 MB document, which forces O(n²) duplicate-key checks. Exploitation requires the application to parse untrusted YAML with the YAML 1.1 schema (yaml.load(input, { schema: yaml.YAML11_SCHEMA })), under which the !!omap tag is resolved.