Tailscale 1.104.4 Fixes SSH Forwarding Flaws That Could Enable Root Access

Summary

Tailscale 1.104.4 fixes SSH forwarding flaws that could let an attacker on a policy-authorized device reach root-only sockets. Users should update or temporarily disable forwarding; no real-world exploitation is reported.

Key points

The flaws affected Tailscale SSH socket forwarding, where a root-running process checked a socket path before operating on it; a timing trick could replace the path after the check.
An attacker needed control of a device already permitted by network policy to open an SSH session with forwarding allowed.
In lab tests, researcher Erica Windisch used forwarding to the Docker control socket to obtain a root shell and read /etc/shadow.
Tailscale 1.104.4 changes forwarding to run as the logged-in user and rely on operating-system file permissions.
Tailscale SSH users should update to version 1.104.4 or later. As a temporary workaround, administrators can set TS_SSH_DISABLE_FORWARDING=1 and restart the tailscaled service.
Windisch's report says headscale grants forwarding on every accepted SSH session and that version 0.29.5 does not fix the reported issues.
Neither Tailscale nor the report says the flaws have been exploited in real attacks; proof-of-concept code is not public, and the four bulletins have no CVE identifiers or severity scores.

Article Details

Vulnerability Types: Time-of-check to time-of-use race condition in Unix socket forwarding path validation
Privilege escalation to root
Severity: Tailscale called the issues serious security issues; no severity scores were reported.
Exploitation Status: not_reported
Exploit Availability: claimed_or_private
Patch Status: partial
Workarounds: Set TS_SSH_DISABLE_FORWARDING=1 in the tailscaled service environment and restart the service.
Restrict SSH access rules to only the users and devices that need access; the report also found single device-to-device rules limited spread in its tests.