CVE-2026-109869: undici vulnerable to Denial of Service via unhandled error on excessive content-encodings

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-15 · updated 2026-10-19
Weakness: CWE-248

Description

undici is an HTTP client library for Node.js. In versions 6.23.0 through 6.29.0, 7.18.0 through 7.30.0, and 8.0.0 through 8.12.1, its fetch() implementation 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 because of 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, so the early close surfaces a content-length mismatch on the orphaned 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, resulting in a denial of service. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, and users should upgrade to one of those versions or later. There is no workaround.

Affected products

undici: from 6.23.0 before 6.29.1; from 7.18.0 before 7.30.1; from 8.0.0 before 8.12.2 — fixed in 6.29.1, 7.30.1, 8.12.2
Npm Undici: from 6.23.0 before 6.29.1; from 7.18.0 before 7.30.1; from 8.0.0 before 8.12.2 — fixed in 6.29.1, 7.30.1, 8.12.2

How to fix

Upgrade to a fixed version: undici 6.29.1, 7.30.1, 8.12.2; Npm Undici 6.29.1, 7.30.1, 8.12.2. Check the vendor advisory for mitigations.

References

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