# 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.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 May 2026
- **Updated:** 15 Sep 2026
- **Also known as:** ALPINE-CVE-2026-5545, AZL-86664, AZL-86928, BELL-CVE-2026-5545, CLSA-2026-1778889816, CLSA-2026-1778890582, CURL-CVE-2026-5545, DEBIAN-CVE-2026-5545, ECHO-ec69-c7b1-4f74, GHSA-6g7g-56fm-f8mp, JLSEC-2026-1204, MINI-mwmc-c375-m54v, MINI-rf72-cmw9-g66x, ROOT-OS-DEBIAN-11-CVE-2026-5545, ROOT-OS-DEBIAN-12-CVE-2026-5545, UBUNTU-CVE-2026-5545

## 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...

Weakness: CWE-613 (DEPRECATED: Insufficient Session Expiration), CWE-305 (Authentication Bypass by Primary Weakness)

## Which versions are affected by CVE-2026-5545?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2026-5545?

Upgrade to a fixed version.

## 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

- [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-2026-5545 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-5545 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-2026-5545/ (Markdown: https://insights.sbomify.com/CVE-2026-5545/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-5545
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-5545
- OSV: https://osv.dev/vulnerability/CVE-2026-5545

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-5545/
Summaries are generated and may contain mistakes; the official description above is the record.