Vulnerability · Published Sep 1, 2026 · Assigned by GitHub_M

CVE-2026-84375js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources

High 7.5

In plain English

A high-severity uncontrolled resource consumption in js-yaml from nodeca. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 46% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.5%top 54.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2, 4.3.2, and 5.4.1, maxTotalMergeKeys in lib/js-yaml/loader.js and lib/loader.js does not count empty mapping sources while processing the merge key <<. An attacker can alias a large sequence of empty mappings into many merge targets, causing O(N * K) processing while totalMergeKeys remains unchanged and the configured resource limit is never reached. A relatively small YAML document can therefore cause prolonged CPU consumption in applications that parse untrusted YAML, and merge processing is enabled by default on these release lines. In v3 & v4, merge is enabled by default so the severity score is higher. This issue is fixed in versions 3.15.2, 4.3.2, and 5.4.1.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	node-js-yaml	no fix listed	DEBIAN-CVE-2026-84375
Debian:13	node-js-yaml	no fix listed	DEBIAN-CVE-2026-84375
Debian:14	node-js-yaml	4.3.2+~4.0.9-1	DEBIAN-CVE-2026-84375
Ubuntu:22.04:LTS	node-js-yaml	no fix listed	UBUNTU-CVE-2026-84375
Ubuntu:24.04:LTS	node-js-yaml	no fix listed	UBUNTU-CVE-2026-84375
Ubuntu:26.04:LTS	node-js-yaml	no fix listed	UBUNTU-CVE-2026-84375
Ubuntu:26.10	node-js-yaml	no fix listed	UBUNTU-CVE-2026-84375
npm	js-yaml	4.3.2	GHSA-2883-xcg3-v3hh
npm	js-yaml	3.15.2	GHSA-2883-xcg3-v3hh

Affected products (as reported)

Vendor	Product	Versions
nodeca	js-yaml	>= 3.0.0, < 3.15.2>= 4.0.0, < 4.3.2>= 5.0.0, < 5.4.1

Weakness: CWE-400, CWE-407 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh x_refsource_CONFIRM
https://github.com/nodeca/js-yaml/pull/797 x_refsource_MISC
https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639 x_refsource_MISC
https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480 x_refsource_MISC
https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b x_refsource_MISC
https://github.com/nodeca/js-yaml/releases/tag/3.15.2 x_refsource_MISC
https://github.com/nodeca/js-yaml/releases/tag/4.3.2 x_refsource_MISC
https://github.com/nodeca/js-yaml/releases/tag/5.4.1 x_refsource_MISC