Researcher publishes unpatched flaws in Tailscale SSH that could allow root access

Researcher Erica Windisch, of Cyberdione Labs, published the “Tailworm” report on 25 October, with 11 security findings in Tailscale, a private networking service widely used to connect servers and devices, and in headscale, a compatible self-hosted control server. According to the report, the tests were carried out in a lab between 22 and 24 October on Tailscale 1.104.2 and headscale 0.29.5.

The main finding affects socket forwarding in Tailscale SSH. According to the author, Tailscale's SSH server runs as root and does not drop privileges when forwarding connections, so from an authorised, compromised device root access could be obtained on another server if the SSH rules allow forwarding. According to The Hacker News, there is no need to steal passwords or keys, but the attacker must already control a device with permission to connect to the target.

According to The Hacker News, there is no security bulletin, CVE or fixed version, and no real-world exploitation is known; Tailscale's bulletins page lists none about this report. Tailscale's vice president of Engineering, Mike Shaver, wrote on Reddit that the company received the report, that it was already reviewing those areas with outside specialists and that it has found problems it is working to fix, although it does not recommend disabling Tailscale SSH across the board, according to that outlet.

The manner of disclosure is disputed: the author describes it as notified but not coordinated and says she sent the report to Tailscale on the Saturday before publishing it. Some researchers question whether the flaws can spread from machine to machine, as the report's name suggests. The report recommends, among other measures, disabling forwarding in the SSH rules and limiting permissions by pairs of devices.

The findings are based solely on the author's report: no other researcher has reproduced them and Tailscale has not confirmed the technical details, according to The Hacker News. It is not known when a fix will be available.