CVE-2026-9675 — undici
HIGHCVE-2026-9675 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
undici WebSocket client vulnerable to denial of service via cumulative fragment bypass
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-2026-9675.
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-2026-9675 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 379,145 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.
undicinpmDescription
Impact
The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.
Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.
Patches
Upgrade to undici >= 8.5.0.
Workarounds
No workaround is available. The fix must be applied through an upgrade.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | ≥ 8.0.0&&< 8.5.0 | 8.5.0npm install undici@8.5.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for undici, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update undici to 8.5.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-9675 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-9675 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-9675. 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.
This is rated Moderate by Red Hat (CVSS 5.9) because successful exploitation requires the undici WebSocket client to connect to an attacker-controlled server (AC:H), which is unlikely in typical Red Hat product deployments where WebSocket endpoints are trusted internal services. No Red Hat product is affected — all…
Red Hat products that bundle the undici HTTP client ship versions 5.x, 6.x, and 7.x, which do not contain the vulnerable WebSocket frame accumulation code path introduced in undici 8.0.0. No Red Hat product streams are affected by this vulnerability. Users who have manually installed undici 8.x outside of Red Hat-provided packages should upgrade to undici 8.5.0 or later to fully resolve this issue.Source: Red Hat security advisory for CVE-2026-9675 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Hardened Images | nodejs26-main-26.3.0-1.2.hum1 | RHSA-2026:22380 |
| Red Hat Hardened Images | rust-main-1.96.0-1.hum1 | RHSA-2026:22934 |
| Red Hat Hardened Images | nodejs24-main-24.16.0-1.hum1 | RHSA-2026:25561 |
| Red Hat Hardened Images | nodejs25-main-25.9.0-1.1.hum1 | RHSA-2026:7378 |
Frequently Asked Questions
Is CVE-2026-9675 in your dependencies?
O3 Security finds CVE-2026-9675 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.