Tailscale Readies Client Patch After 'Tailworm' SSH Flaws Go Public Unpatched

Tailscale is preparing a client update for privilege escalation weaknesses in Tailscale SSH after details went public over the weekend, before any fixes had been released. The findings, dubbed Tailworm, come from Cyberdione Labs and cover version 1.104.2 of the Tailscale client and version 0.29.5 of headscale, the self-hosted open source control server. Six findings are rated high severity, and four concern Tailscale SSH.

According to the report, Tailscale SSH performs some forwarding operations with root privileges, and the safeguards meant to restrict them can be bypassed. An attacker who has already compromised one device could use this against any server that device may reach over Tailscale SSH, provided the access rule allows forwarding. In lab tests this yielded root access on target servers and theft of keys that can add rogue devices to the network. The researchers showed the flaws are wormable: with no user credentials involved, an automated chain moved across every server the policy granted SSH access to, at under a second per hop and without user interaction.

The report also describes issues in an experimental app connector feature, the Serve feature, headscale and the client's relay component, which it says could be used to reach cloud metadata services and internal networks while bypassing access rules, expose a node's administrative interface to remote peers, or cause denial-of-service conditions.

Cyberdione published before patches were available, drawing criticism on social media; the researchers argued rapid awareness would speed remediation. Tailscale VP of Engineering Mike Shaver said on Reddit that the company was already investigating with outside specialists when the report arrived, and that most issues concern what happens after someone is authorized to connect, particularly Unix privilege and SSH forwarding handling. "While it's a serious concern, it isn't the same as an unauthenticated attacker being able to connect to arbitrary machines," he said, adding that impact depends on SSH configuration.

In a Monday update, Tailscale said fixes were in place for most issues and it aimed to release a patched client by the end of Tuesday, October 27, pending testing, with an advisory and technical write-up to follow. The Tailworm report, updated Tuesday, says fixes for several findings have landed in Tailscale's public repositories but none had reached a numbered release at that point. Tailscale said it was not recommending that everyone disable Tailscale SSH. Until the patch arrives, it advises reviewing SSH access policies and disabling SSH forwarding where it isn't needed, which it says mitigates several of the more serious findings. Neither Tailscale nor the report mentions in-the-wild exploitation.