CVE-2023-28436

A vulnerability identified in the implementation of Tailscale SSH in FreeBSD allowed commands to be run with a higher privilege group ID than that specified by Tailscale SSH access rules. **Affected platforms**: FreeBSD **Patched Tailscale client versions**: v1.38.2 or later ### What happened? A difference in the behavior of the FreeBSD `setgroups` system call from POSIX meant that the Tailscale client running on a FreeBSD-based operating system did not appropriately restrict groups on the host when using Tailscale SSH. When accessing a FreeBSD host over Tailscale SSH, the egid of the tailscaled process was used instead of that of the user specified in Tailscale SSH access rules. ### Who is affected? 9 tailnets with 22 FreeBSD nodes running Tailscale SSH since Tailscale v1.34 (released on 2022-12-04) may have had Tailscale SSH sessions with a higher privilege group ID than that specified in Tailscale SSH access rules. We have notified the affected organizations where we have [security contacts](https://tailscale.com/kb/1224/contact-preferences/#setting-the-security-issues-email). ### What is the impact? Tailscale SSH commands may have been run with a higher privilege group ID than that specified in Tailscale SSH access rules if they met all of the following criteria: * The destination node was a FreeBSD device with Tailscale SSH enabled; * Tailscale SSH access rules permitted access for non-root users; and * A non-interactive SSH session was used. ### What do I need to do? If you are running Tailscale on FreeBSD, upgrade to v1.38.2 or later to remediate the issue. Admins of a tailnet can view [FreeBSD nodes with unpatched versions](https://login.tailscale.com/admin/machines?q=version%3A%3C1.38.2+freebsd) in the admin console. To update the local ports tree in advance of what's available upstream, you can: 1. `cd /usr/ports/security/tailscale` 2. edit the Makefile to set `PORTVERSION` to `1.38.2` 3. `make makesum` 4. `make install` Tailscale SSH on other platforms is not affected. ### Credits We would like to thank [Ryan Belgrave](https://www.linkedin.com/in/rbelgrave/) for reporting this issue. ### References * [TS-2023-003](https://tailscale.com/security-bulletins/#ts-2023-003)

Non-interactive Tailscale SSH sessions on FreeBSD may use the effective group ID of the tailscaled process in tailscale.com