James Klein

**Name of the Vulnerable Software and Affected Versions** Rex versions prior to 1.16.2 **Description** The software accepts unknown SSH host keys during remote rsync transfers because the `sync` function hardcodes the `StrictHostKeyChecking=no` option. This occurs across all remote branches of `sync`, including those used for password authentication, private-key authentication, and fallback mechanisms. Since options configured via `set openssh opt()` do not apply to this specific command, host key checking cannot be restored. An attacker capable of redirecting the connection before the legitimate host key is established can present a malicious key, leading to the disclosure of connection passwords during password authentication, the unauthorized upload of local files, or the writing of malicious data to a local destination during downloads. **Recommendations** Update to version 1.16.2 or later.

Net::LibSSH versions before 0.004 for Perl authenticate to an unverified server because connect never checks the host key against known hosts. connect reports success as soon as ssh connect returns SSH OK. libssh leaves the known-hosts check to the application, and this binding never makes it, so the strict hostkeycheck and knownhosts options are set on the session and then decide nothing. Password, agent and public-key authentication, channel and SFTP operations all run on a session whose peer was never identified, so an attacker who can redirect the connection receives the password when password authentication is used, and commands and data sent over the session.