CVE-2026-86411
Description
A flaw was found in curl that can allow unauthorized access through improper session reuse. When an unencrypted File Transfer Protocol (FTP) transfer reuses a pooled connection previously authenticated with a client certificate and upgraded using Transport Layer Security (TLS), curl fails to perform a new handshake or authentication. As a result, the subsequent transfer operates under the prior session's identity, allowing it to perform operations on the remote server with unintended authorization.
Statement
This vulnerability is rated as Low impact by Red Hat because triggering it requires an uncommon sequence of operations where a client application shares a connection pool across both certificate-authenticated FTP sessions and unauthenticated cleartext transfers. In typical enterprise environments, FTP transfers utilizing client certificate authentication are exceptionally rare, substantially constraining real-world attack scenarios. Consequently, exploitation is confined to custom applications specifically designed to reuse connection caches across transfers with mismatched security postures.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | N/A | 9.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | None | N/A | High |
| Availability Impact | None | N/A | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Acknowledgements
Red Hat would like to thank Stanislav Fort (Aisle Research) for reporting this issue.
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