Tailscale Rushes Patches After Uncoordinated Disclosure of ‘Tailworm’ Flaws
Tailscale is preparing to release a client update to address privilege escalation weaknesses in its Tailscale SSH service after the flaws were disclosed over the weekend.
The vulnerabilities, detailed in a report by Cyberdione Labs, affect version 1.104.2 of the Tailscale client and version 0.29.5 of Headscale, an open source control server. The flaws were disclosed before patches were available, drawing criticism on social media but prompting a rapid response from the vendor.
Tailscale provides a mesh VPN service that uses the WireGuard protocol to connect devices and services over a private, peer-to-peer network. The Tailworm report lists 11 findings, with six rated high severity and four specifically concerning Tailscale SSH.
The SSH vulnerabilities allow an attacker who has compromised one device to exploit the flaws against any server that device is permitted to reach over Tailscale SSH, provided the access rule allows forwarding. In lab tests, this resulted in root access on target servers and the theft of keys that can be used to add rogue devices to the network.
Researchers demonstrated that these SSH flaws are wormable. An automated attack chaining these bugs moved from machine to machine across every server the policy granted SSH access to, at under a second per hop and with no user interaction.
The Tailworm report also describes flaws in an experimental app connector feature, the Serve feature, Headscale, and the client’s relay component. These could be exploited 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 (DoS) conditions.
Most of the issues we’ve identified so far concern what happens after someone has been authorized to connect, particularly how Unix privileges and SSH forwarding are handled. In some cases, a session may be able to do more than the configured local user should be allowed to do.
Tailscale's response and mitigation steps
Tailscale VP of Engineering Mike Shaver said the company was already running its own investigation, with input from outside security specialists, when the report came in. He noted that the issues are not the same as an unauthenticated attacker being able to connect to arbitrary machines, but the potential impact depends on how SSH access is configured.
In an update shared on Monday, Tailscale said fixes were in place for most of the issues and that it was aiming to release a patched client by the end of Tuesday, October 27, pending testing. A security advisory and a technical write-up will follow once the update is out.
The Tailworm report, updated on Tuesday, says fixes for several findings have landed in Tailscale’s public code repositories. None had made it into a numbered release at that point.
Tailscale advises organizations to review their SSH access policies and disable SSH forwarding where it isn’t needed, which it says mitigates several of the more serious findings. The vendor stated that based on its current assessment, it is not recommending that everyone disable Tailscale SSH until the patch arrives.
Neither Tailscale nor the Tailworm report mentions in-the-wild exploitation. The company’s focus is on ensuring the patched client is released and that users understand the importance of reviewing their access configurations.
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