Improper Certificate Validation in undici - CVE-2026-84961
Published: September 6, 2026
Vulnerability identifier: #VU147176
CSH Severity: Medium
CVSS v4: 9.1 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-84961
CWE-ID: CWE-295
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass custom TLS certificate validation.
The vulnerability exists due to improper certificate validation in undici BalancedPool when forwarding function-valued connect or tls options to per-upstream pools. A remote attacker can present a TLS certificate that is rejected by a configured custom checkServerIdentity callback but accepted by Node.js default hostname and chain validation to bypass custom TLS certificate validation.
Only applications using BalancedPool with a function-valued connect or tls option, such as a custom checkServerIdentity callback or connector, are affected.
Affected software
undici
How to mitigate CVE-2026-84961
Install security update from vendor's website.
undici - addressed in versions 7.29.1, 8.10.2