CVE-2026-19931 Negotiate ambient user conn reuse
libcurl may reuse authenticated connections for unauthenticated requests, allowing attackers to intercept or send data as another user.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-19931?
CVE-2026-19931 is a critical authentication bypass vulnerability in Haxx Curl, published on 6 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A flaw in libcurl makes it wrongly reuse an HTTP connection setup for a given hostname using Negotiate authentication, when the initial request is done using empty credentials. This can make user B's request get sent over user A's previously authenticated connection.
Weakness: CWE-488
Which versions are affected by CVE-2026-19931?
It affects 1 product.
Products include Haxx Curl.
How do I fix CVE-2026-19931?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-19931 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-19931 exists.
Other vulnerabilities in Haxx Curl
Sources
Also known as ALPINE-CVE-2026-19931, AZL-99752, AZL-99777, AZL-99792, AZL-99819, AZL-99843 and 14 more.