Ansible FreeBSD Jail Connection Plugin: Jail escape via symlink following in put_file (host-side root mv)

Through version 1.3.0, the jailexec connection plugin's put_file resolved a transfer's destination to a path on the jail host (<jail filesystem root> + <destination>) and ran mkdir -p and mv there as root on the host. Those commands follow symbolic links, and the path was operated on outside the jail, so a symlink existing inside the jail was followed by the host-side, root-privileged mv.

A party controlling content inside a managed jail (the jail's root, or any process able to create a symlink in a directory an Ansible task later writes to) can therefore cause an arbitrary root-owned write on the host, outside the jail — a full jail escape. Arbitrary root-owned host writes are readily escalated to host compromise (e.g. cron, rc.d, authorized_keys).

Preconditions: the operator runs a copy/template/fetch-style task (anything using put_file) against the jail, and the attacker can place a symlink inside the jail at or above the task's destination before the transfer runs.

Patches: Fixed in 2.0.0. File transfers now run inside the jail via jexec (mkdir -p <dir> && cat > <dest> for put_file; cat < <src> for fetch_file), so every path resolves within the jail's chroot. An in-jail symlink can at most redirect within the same jail and can no longer reach the host.

Workarounds: None in affected versions; upgrade to 2.0.0.