Vulnerability-Lookup

TS-2026-009

Vulnerability from tailscale - Published: Mon, 13 Jul 2026 00:00:00 GMT

Description: Insecure command line argument handling in Tailscale SSH permitted root user access in violation of ACLs.

What happened?

Tailscale SSH previously accepted usernames that contained a leading - character. On Linux platforms these usernames were passed as arguments to getent(1) to retrieve the corresponding passwd entry, where they were interpreted as flags permitting attacker-controlled behavior. Specifically, if a user connected with the username -i this would have been interpreted as --no-idn and getent would have printed the entire passwd file contents starting with the root user, causing Tailscale to open an interactive root session.

Tailscale SSH now rejects usernames with leading dashes.

This vulnerability is fixed in Tailscale version 1.98.9 or newer.

What was the impact?

A user with SSH access to a Linux node would have been able to obtain a root session by connecting with the username -i, in violation of ACL policy.

Who was affected?

Users of Tailscale SSH on Linux hosts that rely on autogroup:nonroot user restrictions in Tailscale ACLs.

What do I need to do?

If you use Tailscale SSH, upgrade to Tailscale version 1.98.9 or newer.

Credits

We would like to thank Anthropic and Ada Logics for reporting this issue.

Show details on source website

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  "published": "Mon, 13 Jul 2026 00:00:00 GMT",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

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