# CVE-2026-11856: curl libcurl cross-origin Digest authentication state leak

Source: https://junglewise.ai/threats/cve-2026-11856-curl-libcurl-cross-origin-digest-authentication-state-leak  
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-2026-11856 · Severity: info · Published 2026-07-03

A vulnerability in the libcurl library, which is widely used by applications to transfer data over the internet, could allow a malicious server to impersonate a user. When an application uses the same connection handle to talk to a secure site and then a second site, libcurl may mistakenly send the first site's security credentials to the second one. This could allow the second site to reuse those credentials to access the user's account on the original secure site.

## Quick answers

**Is CVE-2026-11856 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-11856 being exploited in the wild.

**How severe is CVE-2026-11856?** Informational severity, published 3 July 2026.

**Which products and versions are affected?** curl curl 7.10.6 to 8.20.0.

**Is there a fix for CVE-2026-11856?** 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-2026-11856 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-11856?** 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 cross-origin state leak exists in libcurl's Digest authentication implementation. When a single easy handle is used for a transfer to 'hostA' using Digest authentication and subsequently reused for a transfer to 'hostB', libcurl fails to clear the authenticated state. Consequently, the 'Authorization:' header intended for 'hostA' is incorrectly transmitted to 'hostB'. An attacker controlling 'hostB' could capture this header and attempt to replay it to impersonate the client on 'hostA'. This issue is specific to the libcurl library and does not affect the curl command-line tool. The vulnerability is mitigated by the fact that the header does not reveal the identity of 'hostA' and credentials themselves are not directly exposed, limiting the attack to replaying specific requests.

## Affected products

- curl curl 7.10.6 to 8.20.0

## Timeline

- 2026-06-10: disclosed: Reported to the curl project via HackerOne.
- 2026-06-24: patched: Fixed in curl version 8.21.0.
- 2026-06-24: advisory: Project curl security advisory published.

## References

- [https://curl.se/docs/CVE-2026-11856.html](https://curl.se/docs/CVE-2026-11856.html)
- [https://curl.se/docs/CVE-2026-11856.json](https://curl.se/docs/CVE-2026-11856.json)
- [https://hackerone.com/reports/3793260](https://hackerone.com/reports/3793260)