An HTTP proxy can trick libcurl into sending the origin's credentials (Basic password, or a Negotiate/Kerberos ticket) to the proxy itself, by answering the `CONNECT` tunnel request with 401 `WWW-Authenticate:` instead of the expected 407 `Proxy-Authenticate:`.
CVE-2026-86414
CVSS base score
9.1 (v3.1)
Severity
CRITICAL
Attack vector
Network
Weakness
CWE-201
Last modified
October 30, 2026
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N