CVE-2026-84375: CWE-400: Uncontrolled Resource Consumption in nodeca js-yaml
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.
CVSS v3.1
Score 7.5high
Affected software
nodeca
js-yaml
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in js-yaml arises because the maxTotalMergeKeys limit does not count empty mapping sources while processing the merge key <<. An attacker can exploit this by aliasing a large sequence of empty mappings into many merge targets, causing O(N * K) processing time while the resource limit remains unchanged. This leads to excessive CPU consumption in applications that parse untrusted YAML with merge processing enabled by default in affected versions. The flaw affects versions >=3.0.0 <3.15.2, >=4.0.0 <4.3.2, and >=5.0.0 <5.4.1 and is resolved in versions 3.15.2, 4.3.2, and 5.4.1.
Potential Impact
This vulnerability can cause denial of service through prolonged CPU consumption when processing specially crafted YAML documents. It does not impact confidentiality or integrity but affects availability by exhausting CPU resources. The severity is rated high with a CVSS score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Mitigation Recommendations
Upgrade js-yaml to version 3.15.2, 4.3.2, or 5.4.1 or later where this issue is fixed. No other mitigations are indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-09-01T16:27:58.129Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Threat ID: 6a97492dacd9273b493ed290
Added to database: 09/01/2026, 21:52:45 UTC
Last enriched: 09/29/2026, 02:03:58 UTC
Last updated: 10/16/2026, 06:48:19 UTC
Views: 106
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