CVE-2026-59869: js-yaml: YAML merge-key chains can force quadratic CPU consumption

highCVSS 7.5CVE-2026-59869

CSIRTS triage

vendor: js-yaml product: js-yaml Denial of service

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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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.5
Published: 2026-07-02
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-59869

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-598690.35% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 27% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-59869	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

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

Recent advisories for js-yaml

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-59870: js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.1, YAML11_SCHEMA support…nvd · 2026-07-08
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
mediumCVE-2026-59868: js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are e…nvd · 2026-07-08