Uptime Kuma Authenticated remote code execution via TailscalePing
Summary
The runTailscalePing method of the TailscalePing class injects the hostname parameter inside a shell command, leading to a command injection and the possibility to run arbitrary commands on the server.
Details
When adding a new monitor on Uptime Kuma, we can select the "Tailscale Ping" type. Then we can add a hostname and insert a command injection payload into it. The front-end application requires that the field follow a specific pattern, this validation only happens on the front-end and can be removed by removing the attribute pattern on the input element.
https://github.com/louislam/uptime-kuma/blob/dc4242019331e65a79ac16deef97510144e01b12/server/monitor-types/tailscale-ping.js#L40-L46
We can finally add the new monitor and observe that our command is being executed.
NOTE: When using Uptime Kuma inside a container, the "TailScale Ping" type is not visible. We can fake this information by intercepting WebSocket messages and set the isContainer option to false.
PoC
- Authenticate.
- Create a new monitor.
- Select the TailScale Ping type (if not visible, see the note in the details section).
- Insert the command injection payload inside the
hostnamefield. (for example$(id >&2)) - Remove the
patternrequirement on the field. - Save and start the monitor.
Impact
An authenticated user can execute arbitrary command on the server running Uptime Kuma.
Remediation
There are other command execution in the codebase, they use a method spawn from the child_process module which does not interpret the command as a shell command, the same thing should be done here.
NOTE: The Tailscale CLI seems to support the -- sequence. It should be used between the ping subcommand and the hostname argument to avoid argument injection.
| Software | From | Fixed in |
|---|---|---|
uptime-kuma
|
1.23.0 | 1.23.7 |
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