Vulnerability in js-yaml (CVE-2026-53550)
Summary
Vulnerability in js-yaml (CVE-2026-53550). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 3.15.0 or later.
Original description
The description as published by the source.
Summary
A crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence.
This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service.
Details
The issue is in merge handling inside lib/loader.js:
storeMappingPair(...)iterates every element of a merge sequence when key tag istag:yaml.org,2002:merge.- For each element, it calls
mergeMappings(...). mergeMappings(...)computesObject.keys(source)and performs_hasOwnProperty.call(destination, key)checks for each key.
When input is of the form:
a: &a {k0:0, k1:0, ..., kK:0}
b: {<<: [*a, *a, *a, ... repeated M times ...]}
all *a entries refer to the same anchored object. After the first merge, subsequent merges are semantically no-ops, but the parser still reprocesses all keys each time.
Resulting work is O(K * M), while input size is O(K + M), giving quadratic scaling as payload grows.
Relevant code path:
lib/loader.js in storeMappingPair(...) merge branch (keyTag === 'tag:yaml.org,2002:merge')
lib/loader.js mergeMappings(...)
Root cause
File: lib/loader.js
Function: storeMappingPair(state, _result, overridableKeys, keyTag, keyNode,
valueNode, startLine, startLineStart, startPos)
Lines: ~359-366
if (keyTag === 'tag…
Source: GitHub Security Advisories (Global) 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-2026-53550 has been found in js-yaml.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade js-yaml to 3.15.0 or later.
If unsure, ask your IT team or search "js-yaml CVE-2026-53550" on the vendor's site.
CVE-2026-53550 (js-yaml) — CWE-407 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 3.15.0 — 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.
Check the vendor advisory for the affected versions of js-yaml.
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.
Update to 3.15.0.
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 3.15.0ステージング環境で 3.15.0 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
- Debian DEBIAN-CVE-2026-53550 node-js-yaml
- Ubuntu UBUNTU-CVE-2026-53550 node-js-yaml
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com