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MEDIUM

bad reuse of HTTP Negotiate connection

Published Mar 11, 2026

Description

libcurl can in some circumstances reuse the wrong connection when asked to do an Negotiate-authenticated HTTP or HTTPS request.

libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead.

When reusing a connection a range of criterion must first be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials. One underlying reason being that Negotiate sometimes authenticates *connections* and not *requests*, contrary to how HTTP is designed to work.

An application that allows Negotiate authentication to a server (that responds wanting Negotiate) with `user1:password1` and then does another operation to the same server also using Negotiate but with `user2:password2` (while the previous connection is still alive) - the second request wrongly reused the same connection and since it then sees that the Negotiate negotiation is already made, it sends the request over that connection thinking it uses the user2 credentials when it is in fact still using the connection authenticated for user1...

The set of authentication methods to use is set with `CURLOPT_HTTPAUTH`.

Applications can disable libcurl's reuse of connections and thus mitigate this problem, by using one of the following libcurl options to alter how connections are or are not reused: `CURLOPT_FRESH_CONNECT`, `CURLOPT_MAXCONNECTS` and `CURLMOPT_MAX_HOST_CONNECTIONS` (if using the curl_multi API).

Affected products

Remediation

Red Hat mitigation

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Weaknesses (2)

CWE-303

CWE-305

References (6)

Change history (0)

No recorded changes yet.

Sources
CVE.org / MITRE
Status PUBLISHED
Assigner curl
Published Mar 11, 2026
Updated Sep 15, 2026
Reserved Feb 5, 2026
Link CVE-2026-1965
CISA Vulnrichment
Updated Mar 11, 2026
NVD
Status Modified
Modified Sep 15, 2026
Link CVE-2026-1965
Red Hat
Severity Moderate
Public date Mar 11, 2026
Links CVE-2026-1965 - Bugzilla