CVE-2026-53550 — js-yaml
MEDIUMCVE-2026-53550 is a medium-severity (CVSS 5.3) CWE-407 vulnerability in js-yaml. A fix is available for js-yaml — see the affected versions and patch details below.
js-yaml: Quadratic-complexity DoS in merge key handling via repeated aliases
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53550.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-53550 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
js-yamlnpmDescription
js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0 and 3.15.0, 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. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0 and 3.15.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | js-yaml | ≥ 4.0.0&&< 4.2.0 | 4.2.0npm install js-yaml@4.2.0 |
| 📦npm | js-yaml | all versions | 3.15.0npm install js-yaml@3.15.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for js-yaml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update js-yaml to 4.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53550 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-53550 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-53550. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat rates this flaw as Moderate impact, consistent with the upstream CVEORG assessment. The vulnerability causes CPU exhaustion via quadratic merge-key processing in js-yaml's YAML parser. In Red Hat products, all confirmed vulnerable code paths run client-side in the browser (OpenShift Console plugins, Kiali…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Hardened Images | nodejs26-main-26.4.0-1.3.hum1 | RHSA-2026:33866 |
| Red Hat Hardened Images | nodejs25-main-25.9.0-1.3.hum1 | RHSA-2026:37534 |
| Red Hat Hardened Images | nodejs24-main-24.18.0-0.3.hum1 | RHSA-2026:38236 |
| Red Hat OpenShift AI 2.25 | rhoai/odh-dashboard-rhel9:1788312226 | RHSA-2026:65126 |
| Red Hat OpenShift AI 3.4 | rhoai/odh-dashboard-rhel9:1787347991 | RHSA-2026:60520 |
| Red Hat Openshift Data Foundation 4.18 | odf4/cephcsi-rhel9:1786705347 | RHSA-2026:56431 |
Frequently Asked Questions
Is CVE-2026-53550 in your dependencies?
O3 Security finds CVE-2026-53550 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.