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CVE-2026-18149

MEDIUMCVSS 5.9/10EPSS 0.31%

Last modified

CVE-2026-18149 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. undici's retry handler can leave an already-exposed response body pending forever. When a server returns a successful response that declares a Content-Length, sends only part of the body, and closes the connection, the retry handler retries the request. EPSS estimates a 0.31% chance of exploitation in the next 30 days.

Description

undici's retry handler can leave an already-exposed response body pending forever. When a server returns a successful response that declares a Content-Length, sends only part of the body, and closes the connection, the retry handler retries the request. If the retry returns a non-retryable status such as 400, the handler forwards that new response downstream and replaces its internal response stream, but the original response body that the application still holds is never ended or destroyed. As a result calls that read that body never settle, and the configured body timeout does not fire because its timer is tied to the connection parser rather than the orphaned body. An attacker-controlled server can trigger this with two short responses without keeping a connection open, and repeated requests accumulate pending promises and streams that can exhaust application concurrency or memory. This affects undici versions from 7.11.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.

Metrics

CVSS 3.1
5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability
0.31%

23.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
NodejsUndici>= 7.11.0, < 7.29.1
NodejsUndici>= 8.0.0, < 8.10.2

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-18149?
undici's retry handler can leave an already-exposed response body pending forever. When a server returns a successful response that declares a Content-Length, sends only part of the body, and closes the connection, the retry handler retries the request. If the retry returns a non-retryable status such as 400, the handler forwards that new response downstream and replaces its internal response stream, but the original response body that the application still holds is never ended or destroyed. As a result calls that read that body never settle, and the configured body timeout does not fire because its timer is tied to the connection parser rather than the orphaned body. An attacker-controlled server can trigger this with two short responses without keeping a connection open, and repeated requests accumulate pending promises and streams that can exhaust application concurrency or memory. This affects undici versions from 7.11.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
How severe is CVE-2026-18149?
CVE-2026-18149 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 0.31% probability of exploitation in the next 30 days.
How do I fix CVE-2026-18149?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST