CVE-2026-5545 wrong reuse of HTTP Negotiate connection
libcurl may incorrectly reuse a Negotiate-authenticated connection for a different user, allowing unauthorized access to resources under the original user's credentials.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-5545?
CVE-2026-5545 is a medium-severity authentication bypass vulnerability in Haxx Curl, published on 13 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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...
Which versions are affected by CVE-2026-5545?
It affects 1 product.
Products include Haxx Curl.
How do I fix CVE-2026-5545?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-5545 being exploited?
There is no known exploitation of CVE-2026-5545 in the wild and no public exploit code.
Other vulnerabilities in Haxx Curl
Sources
Also known as ALPINE-CVE-2026-5545, AZL-86664, AZL-86928, BELL-CVE-2026-5545, CLSA-2026-1778889816, CLSA-2026-1778890582 and 10 more.