CVE-2026-5545

What it is

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host. 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 criteria must 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. An application that first uses Negotiate authentication to a server with `user1:password1` and then does another operation to the same server asking for any authentication method but for `user2:password2` (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data tampering.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-05-13 13:01 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-15 07:16 UTC Last updatedMost recent change to the record

Details

Published

2026-05-13 13:01 UTC

Last modified

2026-09-15 07:16 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-305

Record status

Modified

Affected

• Haxx Curl < 8.20.0

Attack profile CVSS 3.1 · 6.5

Attack vector

Network

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

High

Availability

None