High [CVE-2026-9547] Man-in-the-middle attack via SSH host key bypass

When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and utilizes the `CURLOPT_SSH_KEYFUNCTION` callback, it may silently accept an untrusted server. This vulnerability occurs when a server presents a host key type that does not match the specific key type already recorded for that host in the `known_hosts` file.

Instead of rejecting the mismatch, the callback mechanism fails to properly enforce the restriction, allowing the connection to succeed without warning and risking a potential man-in-the-middle attack. A flaw was found in curl.

The vulnerability requires specific application callback usage, not a general curl client default. Red Hat severity: Important — CVSS 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N).

Weakness: CWE-347. Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4.22; Cert Manager support for Red Hat OpenShift release 1.19; Red Hat Discovery 2; Red Hat Hardened Images; Red Hat OpenShift Dev Spaces 3.30; Red Hat Update Infrastructure 5.

Red Hat lists Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat OpenShift Container Platform 4; Red Hat Trusted Profile Analyzer as not affected.

Affected products named by the advisory: Red Hat package: curl.