CVE-2026-59869

highCVSS 7.5covered by 2 sourcesfirst seen 2026-07-02

js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 before 3.15.0 and from 4.0.0 before 4.3.0, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each mapping merges the previous one. This issue is fixed in versions 3.15.0 and 4.3.0.

CSIRTS triage

What: YAML merge-key chains can force quadratic CPU consumption, leading to denial of service.
Who is affected: Users of js-yaml are affected.
Urgency: Remediation is urgent due to the high severity of the vulnerability.
Action: Update to the latest version of js-yaml.

AI-assisted analysis generated from the source advisory — verify against the original.

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Exploitation outlook

Low exploitation risk0.35% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 27% of all EPSS-scored CVEs.

Advisory coverage (2)

highCVE-2026-59869: js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 before 3.15.0 and from 4.0.0 before…nvd · 2026-07-08
highCVE-2026-59869: js-yaml: YAML merge-key chains can force quadratic CPU consumptionmsrc · 2026-07-02

External references

NVD record for CVE-2026-59869

CVE.org record

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