CVE-2026-85024

undici vulnerable to Denial of Service via unhandled error in WebSocket permessage-deflate decompression

Workarounds

No workaround is available.

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.

CVE-2026-85024 has a CVSS score of 5.9 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.28.1, 7.29.1, 8.10.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to undici v6.28.1, v7.29.1 or v8.10.2.

1. What is CVE-2026-85024? CVE-2026-85024 is a medium-severity security vulnerability in undici (npm), affecting versions >= 6.25.0, < 6.28.1. It is fixed in 6.28.1, 7.29.1, 8.10.2.
2. How severe is CVE-2026-85024? CVE-2026-85024 has a CVSS score of 5.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of undici are affected by CVE-2026-85024? undici (npm) versions >= 6.25.0, < 6.28.1 is affected.
4. Is there a fix for CVE-2026-85024? Yes. CVE-2026-85024 is fixed in 6.28.1, 7.29.1, 8.10.2. Upgrade to this version or later.
5. Is CVE-2026-85024 exploitable, and should I be worried? Whether CVE-2026-85024 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-85024 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-85024?
   • Upgrade undici to 6.28.1 or later
   • Upgrade undici to 7.29.1 or later
   • Upgrade undici to 8.10.2 or later

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