undici vulnerable to Denial of Service via unhandled error in WebSocket permessage-deflate decompressionGHSA-3wwx-pv8p-q78v
MEDIUMFix: nodejs/undici@07c60d9GHSA-3wwx-pv8p-q78v is a medium-severity (CVSS 5.9) CWE-248 vulnerability in undici. A fix is available for undici — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- 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 GHSA-3wwx-pv8p-q78v.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-3wwx-pv8p-q78v by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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
undici's WebSocket client (including Node.js's bundled globalThis.WebSocket) crashes the entire Node.js process when a remote WebSocket peer sends a permessage-deflate compressed message that crosses the decompressed-payload size limit and then contains a malformed DEFLATE block. In lib/web/websocket/permessage-deflate.js, the size-limit cleanup calls removeAllListeners() on the internal zlib InflateRaw, removing its error listener, but leaves the stream running. The inflater then emits a Z_DATA_ERROR with no listener attached, which Node.js treats as a fatal unhandled error event and terminates the process. Application error/close handlers on the public WebSocket cannot observe or prevent this, because the failing object is the internal InflateRaw.
A malicious or compromised WebSocket server can crash a client with a single connection, unauthenticated and without any application mistake. The attack is asymmetric (about 130 KB on the wire expands past the limit) and can be repeated on reconnect (crash loop).
Affected applications are those using the undici WebSocket client (new WebSocket(...)) or Node.js's bundled globalThis.WebSocket that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
Patches
Upgrade to undici v6.28.1, v7.29.1 or v8.10.2.
Workarounds
No workaround is available.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | undici | ≥ 6.25.0&&< 6.28.1 | 6.28.1npm install undici@6.28.1 |
| 📦npm | undici | ≥ 7.28.0&&< 7.29.1 | 7.29.1npm install undici@7.29.1 |
| 📦npm | undici | ≥ 8.1.0&&< 8.10.2 | 8.10.2npm install undici@8.10.2 |
Affected Products
undicinodejsDetection & 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 6.28.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3wwx-pv8p-q78v 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.
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.
A denial of service flaw exists in the undici WebSocket client, which is used by Node.js. A remote, unauthenticated attacker can send a specially crafted compressed WebSocket message that, upon decompression, exceeds a size limit and contains a malformed DEFLATE block. This can lead to an unhandled error and terminate…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for GHSA-3wwx-pv8p-q78v (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Hardened Images | grafana12-4-main-12.4.9-0.6.hum1 | RHSA-2026:63782 |
| Red Hat Hardened Images | nodejs26-main-11.19.1-1.26.8.2.0.1.hum1 | RHSA-2026:66605 |
| Red Hat Hardened Images | nodejs24-main-11.19.0-1.24.21.0.1.hum1 | RHSA-2026:71017 |
Frequently Asked Questions
Is GHSA-3wwx-pv8p-q78v in your dependencies?
Find it across npm, including transitive dependencies.