CVE-2026-94140: Rex versions through 1.16.1 for Perl accept an unknown SSH host key for remote rsync transfers because sync hardcodes StrictHostKeyChecking=no
Rex versions through 1.16.1 for Perl accept an unknown SSH host key for remote rsync transfers because sync hardcodes StrictHostKeyChecking=no.
Every remote branch of sync builds its ssh command with that option, for password authentication, for private-key authentication and for the fallback. The ssh options a caller sets through setopensshopt reach the OpenSSH transport but not this command, so there is no configuration that restores host key checking for the transfer.
An attacker who can redirect the connection before the real host key is known presents their own and the transfer proceeds: under password authentication sync sends the connection password to that server, an upload writes the selected local files to it, and a download writes what it returns to the local destination.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed?
Deployments using Rex through 1.16.1 for Perl are exposed when they use sync for a remote rsync transfer. All remote sync branches are affected, including password authentication, private-key authentication, and the fallback path.
What does an attacker need to exploit this?
An attacker must be able to redirect the SSH connection before the legitimate host key is known and present an attacker-controlled host key. The transfer then proceeds without validating the remote server identity.
Can set_openssh_opt be used to re-enable host key checking for sync transfers?
No. Options configured through set_openssh_opt reach the OpenSSH transport but do not affect the SSH command constructed by sync, which hardcodes StrictHostKeyChecking=no.
What is exposed if exploitation succeeds?
With password authentication, sync sends the connection password to the attacker-controlled server. Uploads send the selected local files to that server, while downloads write attacker-supplied content to the configured local destination.