CVE-2026-59868: js-yaml DoS — Exploit & Fix

Description

js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, 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 version 5.2.0.

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CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0041

Probability of exploitation

0.34%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-407 CWE-407

CWE-770 CWE-770

Affected Products

Vendor	Product	Versions
nodeca	js-yaml	5.0.0 — 5.2.0

References

Advisories & Patches

https://github.com/nodeca/js-yaml/commit/3105455b81dee69e0fd36e09ac0b2ccfdb54adc1 https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv

Exploits

https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv

Other References

https://github.com/nodeca/js-yaml/releases/tag/5.2.0

Frequently Asked Questions

What is CVE-2026-59868? +

js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, 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 version 5.2.0. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-59868? +

CVE-2026-59868 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0041, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-59868? +

CVE-2026-59868 affects products from nodeca, specifically: js-yaml. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-59868? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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