If you found a security vulnerability, you deserve all the credit. Please feel free to have a good ROFLMAO over my broken design. I deserve all the blame and I have all the responsibility for fixing the problem.

I'd like to ask you to fully disclose the details of your valuable findings via GitHub Security Advisory Report a Vulnerability tab or report it privately via [[email protected]] to me.

If you found a severe security vulnerability, a private disclosue is preferred. This is to protect our users from 0-Day exploits. I will always publish vulnerabilities to the public after finding a proper fix.

The public network facing daemon letmeind supports the security hardening technique seccomp.

Seccomp basically disables all Operating System Calls (syscalls) that are not required by the application.

By default seccomp is disabled in letmeind. To enabled it, edit /opt/letmein/etc/letmeind.conf and set the seccomp option:

[GENERAL]
seccomp = kill

Setting the seccomp option to kill will fully enable seccomp. If the letmeind daemon executes a syscall that has not explicitly been allowed by the hard-coded allow-list, the Linux kernel will immediately kill letmeind. That way attacker injected code cannot execute arbitrary syscalls that are not on the allow-list.

Alternatively, you can configure the seccomp option to log. This will not give you any bug-exploit protection, but it will print a kernel log error message, if a syscall is called that is not on the letmein allow-list. This is useful for debugging.

Note that depending on your Linux Distribution you might be getting false seccomp kills, because the allow-list doesn't include a required syscall. In this case, please open a Github Issue on letmein.

Seccomp is currently only supported on the x86_64 and aarch64 CPU architectures.

The seccomp feature of letmeind has been tested with Debian Linux Stable and Unstable.