CVE-2026-45695: Kopia: RCE via SSH ProxyCommand Injection

Kopia’s HTTP server, when started with --without-password , accepts unauthenticated requests to /api/v1/repo/exists. The handler forwards an attacker-supplied storage configuration to blob.NewStorage. For SFTP backends with externalSSH: true, that path constructs a process command line by splitting sshArguments on spaces and passes the result directly to exec.CommandContext("ssh"). An -oProxyCommand=<cmd> token in sshArguments causes OpenSSH to invoke <cmd> via $SHELL -c before any TCP connection is attempted, giving the requester arbitrary command execution as the Kopia process user.