Inconsistent interpretation of HTTP requests in undici - CVE-2026-18540

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Main Vulnerability Database Vulnerabilities #VU147181

Inconsistent interpretation of HTTP requests in undici - CVE-2026-18540

Published: September 6, 2026


Vulnerability identifier: #VU147181
CSH Severity: Low
CVSS v4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-18540
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability: No public exploit available

Vulnerability details

The vulnerability allows a remote attacker to cause downstream response splitting or desynchronization.

The vulnerability exists due to inconsistent interpretation of HTTP response framing in the retry interceptor when resuming a partial response from an attacker-controlled upstream. A remote attacker can cause resumed response bytes to be appended to a partially delivered response body while its original status and headers are retained to cause downstream response splitting or desynchronization.

Exploitation requires interceptors.retry() to be enabled and a downstream forwarder that does not recalculate Content-Length.


Affected software

undici
Automation Assets in IBM Cloud Pak for Integration (CP4I)
Platform Navigator in IBM Cloud Pak for Integration (CP4I)

How to mitigate CVE-2026-18540

Install security update from vendor's website.

undici - addressed in versions 6.28.1, 7.29.1, 8.10.2
Automation Assets in IBM Cloud Pak for Integration (CP4I) - addressed in versions 4.0.26-sc2, 4.4.3
Platform Navigator in IBM Cloud Pak for Integration (CP4I) - addressed in versions 16.1.0.29, 16.2.0.4

External References

Related Security Bulletins