jsyaml CPU DoS via << MergeKey before 3.15.2/4.3.2
CVE-2026-84375 Published on September 1, 2026
js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources
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.
Vulnerability Analysis
CVE-2026-84375 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Types
What is a Resource Exhaustion Vulnerability?
The software does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
CVE-2026-84375 has been classified to as a Resource Exhaustion vulnerability or weakness.
Inefficient Algorithmic Complexity
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
Affected Versions
nodeca js-yaml:- Version >= 3.0.0, < 3.15.2 is affected.
- Version >= 4.0.0, < 4.3.2 is affected.
- Version >= 5.0.0, < 5.4.1 is affected.