# CVE-2026-87861: curl cross-origin reuse of Negotiate connection

Source: https://junglewise.ai/threats/cve-2026-87861-when-using-ambient-user-credentials-an-http-request-directed-to  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-87861 · Severity: info · Published 2026-10-20

curl is a widely-used tool for transferring data with URLs, used by many applications and scripts. When using automatic authentication credentials, a request to one website may be sent over an existing connection that was previously authenticated for a different website, potentially exposing the original request to unintended access. This could allow an attacker to intercept or misuse authentication tokens across different origins.

Technologies: [Curl](https://junglewise.ai/threats/technologies/curl-curl). Vendors: [Curl](https://junglewise.ai/threats/vendors/curl).

## Quick answers

**Is CVE-2026-87861 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-87861 being exploited in the wild.

**How severe is CVE-2026-87861?** Informational severity, published 20 October 2026.

**Which products and versions are affected?** Curl 8.21.0 to 8.22.0.

**Is there a fix for CVE-2026-87861?** Yes: fixed in curl 8.23.0. Until then: Avoid using ambient users for authentication, or upgrade to curl 8.23.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-87861 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-87861?** Check whether you run Curl 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.

## How to fix

- Fixed in curl 8.23.0

Avoid using ambient users for authentication, or upgrade to curl 8.23.0 or later.

## Technical details

An HTTP request targeting one origin may be dispatched over a connection previously authenticated via HTTP Negotiate authentication for a different origin. This occurs when ambient credentials (blank username with OS-level identity) are used, leaving the intended credentials unused and exposing authentication state reuse across origins. The vulnerability is a connection reuse logic flaw (CWE-201: Information Exposure Through Sent Data) affecting versions 8.21.0 through 8.22.0.

## Affected products

- curl curl 8.21.0 to 8.22.0

## Timeline

- 2026-08-26: disclosed: Issue reported to curl project
- 2026-10-14: patched: curl 8.23.0 released with fix
- 2026-10-14: advisory: CVE-2026-87861 advisory published

## References

- [https://curl.se/docs/CVE-2026-87861.html](https://curl.se/docs/CVE-2026-87861.html)
- [https://curl.se/docs/CVE-2026-87861.json](https://curl.se/docs/CVE-2026-87861.json)

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