CVE-2023-28436 is a medium-severity (CVSS 5.7) Improper Privilege Management vulnerability in tailscale.com. A fix is available for tailscale.com — see the affected versions and patch details below.
Non-interactive Tailscale SSH sessions on FreeBSD may use the effective group ID of the tailscaled process
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-28436.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
tailscale.comReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | tailscale.com | ≥ 1.34.0&&< 1.38.2 | 1.38.2go get tailscale.com@v1.38.2 |
Affected Products
tailscaletailscaleDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tailscale.com, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update tailscale.com to 1.38.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-28436 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.
Frequently Asked Questions
Is CVE-2023-28436 in your dependencies?
Find it across Go, including transitive dependencies.