ssh-mitm v4.0 releases: intercepting proxy server for security audits

by do son · Published December 21, 2020 · Updated September 14, 2023

ssh-mitm – intercept ssh traffic

ssh-mitm is an intercepting (mitm) proxy server for security audits.

Redirect/mirror Shell to another ssh client supported in 0.2.8
Replace File in SCP supported in 0.2.6
Replace File in SFTP supported in 0.2.3
Transparent proxy support in 0.2.2! – intercepting traffic to other hosts is now possible when using arp spoofing or proxy is used as a gateway.
Since release 0.2.0, SSH Proxy Server has full support for tty (shell), scp, and sftp!

Feature

session recording
session hijacking
modify files with scp and sftp
authentication passthrough (password and public key)

SSH MITM Attacks

SSH uses trust on first use. This means, that you have to accept the fingerprint if it is not known.

$ ssh -p 10022 hugo@localhost

The authenticity of host '[localhost]:10022 ([127.0.0.1]:10022)' can't be established.

RSA key fingerprint is SHA256:GIAALZgy8Z86Sezld13ZM74HGbE9HbWjG6T9nzja/D8.

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added '[localhost]:10022' (RSA) to the list of known hosts.

If a server fingerprint is known, ssh warns the user, that the host identification has changed.

If the victim accepts the (new) fingerprint, then the session can be intercepted.

Use-Case: Honey Pot

When ssh proxy server is used as a honey pot, attackers will accept the fingerprint, because he wants to attack this machine. An attacker also does not know if the fingerprint is correct and if the key has changed, perhaps it the server was reinstalled and a new key pair was generated.

User-Case: Security Audit

Intercepting ssh during security audits is useful to understand, how an application works.

For example, if you have an application, which connects to your local router via ssh, to configure the device, you can intercept those connections, if the application does not know the fingerprint and accept it on first use.

If the application knows the fingerprint, then the same host key is used on every device. In this case, you have a good chance to extract the host key from a firmware updated and use it to trick the application.

Changelog v4.0

Added

added configuration file to configure default values
added info and PoC exploit for CVE-2023-25136
mosh – added more information for decrypted packet
added json logging format
added client ip and port to client information #145

Fixed

added workarround for git to avoid unexpected session termination when EOF was reveived
added fix for GitHub git operations
fixes #136 – set paramiko version to >=3,<3.2 to fix private api changes in paramiko

Changed

set banner name only for server, not for client
when output is piped to another application, the logformat is switched to json
changed build system to hatch
create AppImage with appimagetool instead of AppImage-Builder

Removed

removed support for Python 3.7
removed official support for Windows

Install

pip install ssh-mitm

Use

Password authentication

Start the server:

ssh-mitm --remote-host 127.0.0.1

Connect to server:

ssh -p 10022 user@proxyserver

Public key authentication

When public-key authentication is used, the agent is forwarded to the remote server.

Start the server:

ssh-mitm --forward-agent --remote-host 127.0.0.1

Connect to server:

ssh -A -p 10022 user@proxyserver

Tutorial

Authors

Manfred Kaiser
Simon Böhm

ssh-mitm v4.0 releases: intercepting proxy server for security audits

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