CVE-2026-84375

01/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.

02/References8

• github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d9…
• github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae2…
• github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578e…
• github.com/nodeca/js-yaml/pull/797
• github.com/nodeca/js-yaml/releases/tag/3.15.2
• github.com/nodeca/js-yaml/releases/tag/4.3.2
• github.com/nodeca/js-yaml/releases/tag/5.4.1
• github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3…