Описание
js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources
Summary
maxTotalMergeKeys does not count empty mappings. An attacker can repeatedly merge a large sequence of them and consume significant CPU without reaching the configured limit.
Example
For every target, the loader iterates all N elements of arr. This results in O(N * K) work while totalMergeKeys remains unchanged.
PoC
Observed results:
| N | YAML size | Time |
|---|---|---|
| 800 | ~13 KB | ~20 ms |
| 3200 | ~50 KB | ~180 ms |
| 20000 | ~500 KB | ~13 s |
Impact
An attacker can submit a relatively small YAML document that causes prolonged CPU consumption despite the default maxTotalMergeKeys limit.
Fix
Count each merge-source mapping as one budget unit, in addition to counting its keys.
Difference with v5
In v3 & v4, merge is enabled by default. So, the severity score is higher.
Ссылки
- https://github.com/nodeca/js-yaml/security/advisories/GHSA-2883-xcg3-v3hh
- https://nvd.nist.gov/vuln/detail/CVE-2026-84375
- https://github.com/nodeca/js-yaml/pull/797
- https://github.com/nodeca/js-yaml/commit/3485bc06ff8a0251505f44a00414d90df2466639
- https://github.com/nodeca/js-yaml/commit/6a8e05f9a485188ed730ac81e81ae221352ef480
- https://github.com/nodeca/js-yaml/commit/d90b6612a5a84385bdcb556c44578eac76dc0f6b
- https://github.com/nodeca/js-yaml/releases/tag/3.15.2
- https://github.com/nodeca/js-yaml/releases/tag/4.3.2
Пакеты
js-yaml
>= 4.0.0, < 4.3.2
4.3.2
js-yaml
>= 3.0.0, < 3.15.2
3.15.2
Связанные уязвимости
(js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15. ...)
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.
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.
js-yaml is a JavaScript YAML parser and dumper. From 3.0.0 until 3.15. ...