# CVE-2026-86415: curl auto client cert connection reuse mixup

Source: https://junglewise.ai/threats/cve-2026-86415-libcurl-s-connection-cache-match-function-never-considers-the  
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-2026-86415 · Severity: info · Published 2026-10-20

libcurl is an open-source library used by applications to handle network communication. When using the Schannel TLS backend on Windows, the library can incorrectly reuse a cached, authenticated connection for a different destination after a redirect, even when client certificate authentication was disabled for the new destination. This could expose sensitive data by sending authentication credentials intended for one server to a different server.

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

## Quick answers

**Is CVE-2026-86415 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86415 being exploited in the wild.

**How severe is CVE-2026-86415?** Informational severity, published 20 October 2026.

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

**Is there a fix for CVE-2026-86415?** Yes: fixed in curl 8.23.0. Until then: Build curl with a different TLS backend instead of Schannel, or apply the upstream patch to your local version. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86415 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-86415?** Check whether you run Curl 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.

## How to fix

- Fixed in curl 8.23.0

Build curl with a different TLS backend instead of Schannel, or apply the upstream patch to your local version.

## Technical details

The connection cache match function in libcurl's Schannel TLS backend fails to consider the automatic client certificate option when reusing cached connections, allowing an already-authenticated connection to be handed to a redirected transfer to a different origin despite explicit configuration to disable auto client cert for that transfer. This is a cross-origin credential leakage issue (CWE-201) affecting only Windows Schannel builds. The flaw requires network access and a redirect scenario; no authentication is required from an attacker.

## Affected products

- curl libcurl 8.21.0 to 8.22.0

## Timeline

- 2026-09-03: disclosed: Issue reported to curl project
- 2026-10-14: patched: curl 8.23.0 released with fix
- 2026-10-14: advisory: CVE-2026-86415 published

## References

- [https://curl.se/docs/CVE-2026-86415.html](https://curl.se/docs/CVE-2026-86415.html)
- [https://curl.se/docs/CVE-2026-86415.json](https://curl.se/docs/CVE-2026-86415.json)

## Related threats

- [libcurl TFTP direction confusion](https://junglewise.ai/threats/cve-2026-92389-libcurl-s-tftp-state-machine-fails-to-validate-state-transitions)
- [curl FTP wildcard write callback mixup](https://junglewise.ai/threats/cve-2026-92388-when-an-ftp-wildcard-list-operation-fails-libcurl-omits-the)