CVE-2026-109869

undici vulnerable to Denial of Service via unhandled error on excessive content-encodings

Workarounds

None.

undici's fetch() crashes the Node.js process when a malicious server returns a response with more than five content codings and closes the connection before sending the body. undici rejects such responses (a content-encoding limit), but it created the internal response stream before that check and returned without attaching an error listener or aborting the request. The early close then surfaces a content-length mismatch on that orphaned internal stream, which Node.js treats as an unhandled error and terminates the process. A remote, unauthenticated server can trigger this with a single response, even when the application correctly catches the fetch() rejection. undici 6.x, 7.x, and 8.x are affected.

CVE-2026-109869 has a CVSS score of 7.5 (High). 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 (6.29.1, 7.30.1, 8.12.2); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

Upgrade to 6.29.1, 7.30.1, or 8.12.2. undici now validates the content-encoding chain before creating the internal body stream and aborts the response when the limit is exceeded, so no error can surface on an orphaned stream.

1. What is CVE-2026-109869? CVE-2026-109869 is a high-severity security vulnerability in undici (npm), affecting versions >= 6.23.0, < 6.29.1. It is fixed in 6.29.1, 7.30.1, 8.12.2.
2. How severe is CVE-2026-109869? CVE-2026-109869 has a CVSS score of 7.5 (High). 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-2026-109869? undici (npm) versions >= 6.23.0, < 6.29.1 is affected.
4. Is there a fix for CVE-2026-109869? Yes. CVE-2026-109869 is fixed in 6.29.1, 7.30.1, 8.12.2. Upgrade to this version or later.
5. Is CVE-2026-109869 exploitable, and should I be worried? Whether CVE-2026-109869 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-2026-109869 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-2026-109869?
   • Upgrade undici to 6.29.1 or later
   • Upgrade undici to 7.30.1 or later
   • Upgrade undici to 8.12.2 or later

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