# CVE-2026-8927: curl libcurl authentication state leak in proxy handle reuse

Source: https://junglewise.ai/threats/cve-2026-8927-curl-libcurl-authentication-state-leak-in-proxy-handle-reuse  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-03. Updated: 2026-07-03  
License: CC BY 4.0 with a link back

CVE-2026-8927 · Severity: info · Published 2026-07-03

A vulnerability in the libcurl library, which is widely used by applications to transfer data over networks, could allow sensitive authentication information to be leaked. When an application reuses a connection handle to talk to different proxy servers, it may accidentally send the login credentials intended for the first proxy to the second one. This could allow a malicious proxy operator to impersonate the user or gain unauthorized access to other network resources.

## Quick answers

**Is CVE-2026-8927 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-8927 being exploited in the wild.

**How severe is CVE-2026-8927?** Informational severity, published 3 July 2026.

**Which products and versions are affected?** curl libcurl 7.12.0 to 8.20.0.

**Is there a fix for CVE-2026-8927?** A patch was published on 2026-06-24: Fixed in curl version 8.21.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-8927 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-8927?** Check whether anything you run is named in the advisory. 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 flaw in libcurl's handle reuse logic occurs when sequential transfers are configured via environment variables. If an initial transfer uses Digest authentication with a specific proxy, libcurl fails to reset the authentication state before a subsequent transfer. If the second transfer is routed through a different proxy, the 'Proxy-Authorization' header containing the authenticated state for the first proxy is leaked to the second. This is classified as CWE-294 (Authentication Bypass by Capture-replay). The vulnerability affects libcurl but not the curl command-line tool. Users are advised to upgrade to version 8.21.0 or avoid handle reuse when switching proxies.

## Affected products

- curl libcurl 7.12.0 to 8.20.0

## Timeline

- 2026-05-18: disclosed: Reported to the curl project via HackerOne
- 2026-06-24: patched: Fixed in curl version 8.21.0
- 2026-06-24: advisory: Project advisory published

## References

- [https://curl.se/docs/CVE-2026-8927.html](https://curl.se/docs/CVE-2026-8927.html)
- [https://curl.se/docs/CVE-2026-8927.json](https://curl.se/docs/CVE-2026-8927.json)
- [https://hackerone.com/reports/3744543](https://hackerone.com/reports/3744543)