# CVE-2026-5545: libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after…

Source: https://junglewise.ai/threats/cve-2026-5545-curl-incorrect-connection-reuse-in-negotiate-authentication  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-14  
License: CC BY 4.0 with a link back

CVE-2026-5545 · Severity: medium · CVSS 6.5 · Published 2026-05-13

A vulnerability in the curl data transfer library could cause an application to send data using the wrong user's credentials. When an application makes multiple authenticated requests to the same server, curl may incorrectly reuse an existing connection established by a different user. This could lead to unauthorized data access or actions being performed under the wrong account identity.

Technologies: [Haxx Curl](https://junglewise.ai/threats/technologies/curl), [Haxx Libcurl](https://junglewise.ai/threats/technologies/libcurl). Vendors: [Haxx](https://junglewise.ai/threats/vendors/haxx).

## Quick answers

**Is CVE-2026-5545 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-5545 being exploited in the wild.

**How severe is CVE-2026-5545?** Medium severity, with a CVSS score of 6.5, published 13 May 2026.

**Which products and versions are affected?** Haxx Curl 7.10.6 to 8.19.0; Haxx Libcurl 7.10.6 to 8.19.0.

**Is there a fix for CVE-2026-5545?** A patch was published on 2026-04-29: Fixed in curl 8.20.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-5545 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-5545?** Check whether you run Haxx Curl or Haxx Libcurl at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A logical error in libcurl's connection pooling mechanism allows for improper connection reuse when Negotiate authentication is involved. If an application performs a Negotiate-authenticated request as one user and subsequently attempts a request to the same host as a different user, libcurl may fail to validate the credential change and reuse the existing authenticated socket. This results in the second request being transmitted over a connection still authorized as the first user. The vulnerability affects versions 7.10.6 through 8.19.0 and is fixed in version 8.20.0. Mitigation is possible by disabling connection reuse via CURLOPT_FRESH_CONNECT.

## Affected products

- haxx curl 7.10.6 to 8.19.0
- haxx libcurl 7.10.6 to 8.19.0

## Timeline

- 2026-04-01: disclosed: Reported to curl project via HackerOne
- 2026-04-29: patched: Fixed in curl 8.20.0
- 2026-04-29: advisory: Project curl advisory published
- 2026-05-13: other: NVD publication date

## References

- [https://curl.se/docs/CVE-2026-5545.html](https://curl.se/docs/CVE-2026-5545.html)
- [https://curl.se/docs/CVE-2026-5545.json](https://curl.se/docs/CVE-2026-5545.json)
- [https://hackerone.com/reports/3642555](https://hackerone.com/reports/3642555)

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