# CVE-2026-86411: curl FTP connection reuse inherits client certificate

Source: https://junglewise.ai/threats/cve-2026-86411-an-ftp-transfer-configured-with-curlusessl-none-can-reuse-a  
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-2026-86411 · Severity: info · Published 2026-10-20

curl is a widely-used library and tool for transferring files over the network using protocols like FTP. When reusing FTP connections across different application components or requests, curl can inadvertently allow a second connection to inherit the client certificate authentication of a previous connection. This means an unauthorized user could gain access under a legitimate client's identity without providing their own credentials.

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

## Quick answers

**Is CVE-2026-86411 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86411 being exploited in the wild.

**How severe is CVE-2026-86411?** Informational severity, published 20 October 2026.

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

**Is there a fix for CVE-2026-86411?** Yes: fixed in curl 8.22.0. Until then: Do not use client certificates for FTP transfers, or upgrade to curl 8.22.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86411 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-86411?** 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 8.22.0

Do not use client certificates for FTP transfers, or upgrade to curl 8.22.0 or later.

## Technical details

An ftp:// transfer configured with CURLUSESSL_NONE can reuse a pooled FTP control connection from a previous easy handle that was upgraded with STARTTLS and authenticated using a client certificate. The second handle performs neither a new TLS handshake nor a new FTP login, so the server continues to authorize it under the first handle's certificate identity (CWE-488: Exposure of Data Element to Wrong Session).

## Affected products

- curl curl 8.21.0

## Timeline

- 2026-08-27: disclosed
- 2026-09-02: patched
- 2026-10-14: advisory

## References

- [https://curl.se/docs/CVE-2026-86411.html](https://curl.se/docs/CVE-2026-86411.html)
- [https://curl.se/docs/CVE-2026-86411.json](https://curl.se/docs/CVE-2026-86411.json)

## Related threats

- [libcurl credentials leak in CURLINFO_EFFECTIVE_URL](https://junglewise.ai/threats/cve-2026-94266-libcurl-could-accidentally-return-a-url-for-curl-easy-getinfo-s)
- [curl Negotiate authentication credential exposure on redirect](https://junglewise.ai/threats/cve-2026-94265-when-processing-an-http-redirect-to-a-url-containing-userinfo-a)
- [curl stack overflow in MIME structure cleanup](https://junglewise.ai/threats/cve-2026-92391-a-deeply-nested-multipart-mime-structure-constructed-via-the)
- [curl remote-header-name file overwrite bypass](https://junglewise.ai/threats/cve-2026-92390-when-invoked-with-remote-header-name-j-curl-fails-to-preserve-its)
- [curl infinite loop via server response omission](https://junglewise.ai/threats/cve-2026-92387-by-permanently-omitting-the-final-control-response-line-a)