Summary
Non-interactive Tailscale SSH sessions on FreeBSD may use the effective group ID of the tailscaled process
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.
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 in the admin console.
To update the local ports tree in advance of what's available upstream, you can:
cd /usr/ports/security/tailscale- edit the Makefile to set
PORTVERSIONto1.38.2 make makesummake install
Tailscale SSH on other platforms is not affected.
Credits
We would like to thank Ryan Belgrave for reporting this issue.
References
Impact
The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access. Typical impact: privilege escalation beyond the intended level.
CVE-2023-28436 has a CVSS score of 5.7 (Medium). The vector is reachable from an adjacent network, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.38.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2023-28436? CVE-2023-28436 is a medium-severity improper privilege management vulnerability in tailscale.com (go), affecting versions >= 1.34.0, < 1.38.2. It is fixed in 1.38.2. The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access.
- How severe is CVE-2023-28436? CVE-2023-28436 has a CVSS score of 5.7 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of tailscale.com are affected by CVE-2023-28436? tailscale.com (go) versions >= 1.34.0, < 1.38.2 is affected.
- Is there a fix for CVE-2023-28436? Yes. CVE-2023-28436 is fixed in 1.38.2. Upgrade to this version or later.
- Is CVE-2023-28436 exploitable, and should I be worried? Whether CVE-2023-28436 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-28436 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-28436? Upgrade
tailscale.comto 1.38.2 or later.