js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2 and 4.3.2, 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. This issue is fixed in versions 3.15.2 and 4.3.2.
Advisories

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Fixes

Solution

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Workaround

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History

Wed, 02 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-835
References
Metrics threat_severity

None

threat_severity

Important


Wed, 02 Sep 2026 00:00:00 +0000

Type Values Removed Values Added
First Time appeared Nodeca
Nodeca js-yaml
Vendors & Products Nodeca
Nodeca js-yaml

Tue, 01 Sep 2026 22:00:00 +0000

Type Values Removed Values Added
Description js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15.2 and 4.3.2, 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. This issue is fixed in versions 3.15.2 and 4.3.2.
Title js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources
Weaknesses CWE-400
CWE-407
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-01T21:43:13.617Z

Reserved: 2026-09-01T16:27:58.129Z

Link: CVE-2026-84375

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-01T22:17:19.440

Modified: 2026-09-01T22:17:19.440

Link: CVE-2026-84375

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-01T21:43:13Z

Links: CVE-2026-84375 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-02T00:30:04Z

Weaknesses