CVE-2026-9547

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.

• curl 8.21.0~rc2-1 (unimportant) https://curl.se/docs/CVE-2026-9547.html Debian builds with --without-libssh --with-libssh2. Introduced with: https://github.com/curl/curl/commit/507cf6a13db0375eadd4655b4c64710db29e9cf2 (curl-7_69_0) Fixed by: https://github.com/curl/curl/commit/0b8dbbc63c98777e4584cb9fbd71df3464008ad1 (rc-8_21_0-1, curl-8_21_0)