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Sending remote procedure calls through e-mail (RPC-Mail)
From: Abe Usher <securitylist () sharp-ideas net>
Date: Tue, 19 Oct 2004 22:26:43 -0400

Have you ever had the need to remotely send a command to a system, but you could not access it directly via ssh or telnet because the firewall is blocking all inbound connections?

The practice of portknocking <http://www.portknocking.org/> provides an interesting network authentication mechanism for establishing a connection to a networked computer that has no open ports (as advertised on portknocking.org).

While I find portknocking ingenious, it is somewhat cumbersome and overly complex for most users. I propose an alternative - send remote procedure calls via e-mail. I've coded an application that fits the bill: RPC-Mail.

The premise of RPC-Mail is simple:
(1) Construct an e-mail message that has a command that you want one of your remote PCs to execute.
(2) Send the e-mail to a special account that is only used by RPC-Mail.
(3) Have the remote PC set up with a scheduled task or cron job to periodically execute the application RPC-Mail.py. (4) When RPC-Mail.py executes, it parses all of the subject lines and message bodies of e-mail messages that it finds. If the message body contains a special passphrase, RPC-Mail executes the subject line as a command, and returns standard output as an e-mail message.

For more information check out my full write up on:

Abe Usher, CISSP

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