Tailscale Patches Tailworm Flaws After Early Disclosure

Tailscale has released fixes for 11 vulnerabilities disclosed by Cyberdione Labs. The flaws, collectively called Tailworm, affect Tailscale client version 1.104.2 and headscale version 0.29.5, an open-source control server that organizations can host themselves.

Six findings received high-severity ratings. Four affect Tailscale SSH, which grants access through device identity and network policy rather than passwords or cryptographic keys. The report found that some SSH forwarding operations run with root privileges and that safeguards limiting those operations can be bypassed.

An attacker who compromises one device could use the flaws against servers that the device is allowed to reach through Tailscale SSH, if the access policy permits forwarding. In laboratory tests, researchers obtained root access on target servers and extracted keys that could be used to add unauthorized devices to the network.

The researchers also chained the SSH flaws into an automated worm. The attack moved from one server to another in less than a second per hop, without user interaction or additional credentials. An initial compromise could result from phishing, a vulnerable web application or a malicious software package.

Other findings affect Tailscale’s experimental app connector, its Serve feature, headscale and the client’s relay component. The reported impacts include access to cloud metadata services and internal networks, exposure of a node’s administrative interface to remote peers, access-rule bypasses and denial-of-service conditions.

Cyberdione Labs published its report before patches were available, drawing criticism over the timing. The researchers argued that early awareness could speed up remediation.

Tailscale Vice President of Engineering Mike Shaver described the company’s response in a Reddit post. Tailscale had begun its own investigation with help from outside security specialists before receiving the report.

“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,” Shaver wrote. “In some cases, a session may be able to do more than the configured local user should be allowed to do.”

Shaver described the issue as serious but different from an unauthenticated attacker gaining access to arbitrary machines. He added that the impact depends on an organization’s SSH access settings.

Tailscale initially said that most fixes were ready and that it planned to release a patched client by the end of Tuesday, Oct. 27, pending testing. The company later published its findings, four security bulletins and remediation guidance. Fixes for several findings also appeared in its public code repositories.

Before the patched release, Tailscale advised organizations to review SSH access policies and disable SSH forwarding where it was not needed. The company did not recommend that all customers disable Tailscale SSH. Neither Tailscale nor Cyberdione Labs reported exploitation of the vulnerabilities in the wild.