# CVE-2026-1965: bad reuse of HTTP Negotiate connection

> libcurl may reuse authenticated connections with wrong credentials, allowing attackers to access data as another user.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Mar 2026
- **Updated:** 15 Sep 2026
- **Also known as:** ALPINE-CVE-2026-1965, AZL-79676, BELL-CVE-2026-1965, CURL-CVE-2026-1965, DEBIAN-CVE-2026-1965, ECHO-3c02-5957-bbd3, GHSA-q9qg-g2c3-3hr2, JLSEC-2026-436, MINI-3rjr-9rfx-rpgc, ROOT-OS-DEBIAN-11-CVE-2026-1965, ROOT-OS-DEBIAN-12-CVE-2026-1965, UBUNTU-CVE-2026-1965

## What is CVE-2026-1965?

CVE-2026-1965 is a medium-severity authentication bypass vulnerability in Haxx Curl, published on 11 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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).

Weakness: CWE-305 (Authentication Bypass by Primary Weakness)

## Which versions are affected by CVE-2026-1965?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2026-1965?

Apply the vendor's patch.

## Is CVE-2026-1965 being exploited?

There is no known exploitation of CVE-2026-1965 in the wild and no public exploit code.

## Other vulnerabilities in Haxx Curl

- [CVE-2026-19931](https://insights.sbomify.com/CVE-2026-19931/): Negotiate ambient user conn reuse (critical 9.8)
- [CVE-2026-10536](https://insights.sbomify.com/CVE-2026-10536/): HTTP/2 stream-dependency tree UAF (critical 9.8)
- [CVE-2026-11856](https://insights.sbomify.com/CVE-2026-11856/): cross-origin Digest auth state leak (critical 9.8)
- [CVE-2026-8925](https://insights.sbomify.com/CVE-2026-8925/): SASL double-free (critical 9.8)
- [CVE-2026-9079](https://insights.sbomify.com/CVE-2026-9079/): stale proxy password leak (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-1965 and fix it if it is affected.

What it is: CVE-2026-1965 is a medium-severity authentication bypass vulnerability in Haxx Curl, published on 11 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-1965 in the wild and no public exploit code.

Affected product: Haxx Curl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-1965/ (Markdown: https://insights.sbomify.com/CVE-2026-1965/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-1965
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-1965
- OSV: https://osv.dev/vulnerability/CVE-2026-1965

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-1965/
Summaries are generated and may contain mistakes; the official description above is the record.