131 lines
3.4 KiB
Ruby
131 lines
3.4 KiB
Ruby
##
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# This module requires Metasploit: http://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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require 'msf/core'
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class MetasploitModule < Msf::Encoder
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Rank = NormalRanking
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def initialize
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super(
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'Name' => 'Perl Command Encoder',
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'Description' => %q{
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This encoder uses perl to avoid commonly restricted characters.
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},
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'Author' => 'hdm',
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'Arch' => ARCH_CMD,
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'Platform' => 'unix',
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'EncoderType' => Msf::Encoder::Type::CmdUnixPerl)
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end
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#
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# Encodes the payload
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#
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def encode_block(state, buf)
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# Skip encoding for empty badchars
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if state.badchars.length == 0
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return buf
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end
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if state.badchars.include?("-")
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raise EncodingError
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else
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buf = encode_block_perl(state,buf)
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end
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return buf
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end
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#
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# Uses the perl command to hex encode the command string
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#
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def encode_block_perl(state, buf)
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hex = buf.unpack("H*").join
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cmd = 'perl -e '
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qot = ',-:.=+!@#$%^&'
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# Convert spaces to IFS...
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if state.badchars.include?(" ")
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if state.badchars.match(/[${IFS}]/n)
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raise EncodingError
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end
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cmd.gsub!(/\s/, '${IFS}')
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end
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# Can we use single quotes to enclose the command string?
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if state.badchars.include?("'")
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if (state.badchars.match(/[()\\]/))
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cmd << perl_e(state, qot, hex)
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else
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# Without quotes, we can use backslash to escape parens so the
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# shell doesn't try to interpreter them.
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cmd << "system\\(pack\\(#{perl_qq(state, qot, hex)}\\)\\)"
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end
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else
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# Quotes are ok, but we still need parens or spaces
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if (state.badchars.match(/[()]/n))
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if state.badchars.include?(" ")
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cmd << perl_e(state, qot, hex)
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else
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cmd << "'system pack #{perl_qq(state, qot, hex)}'"
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end
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else
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cmd << "'system(pack(#{perl_qq(state, qot, hex)}))'"
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end
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end
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return cmd
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end
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def perl_e(state, qot, hex)
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# We don't have parens, quotes, or backslashes so we have to use
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# barewords on the commandline for the argument to the pack
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# function. As a consequence, we can't use things that the shell
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# would interpret, so $ and & become badchars.
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qot.delete("$")
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qot.delete("&")
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# Perl chains -e with newlines, but doesn't automatically add
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# semicolons, so the following will result in the interpreter
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# seeing a file like this:
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# system
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# pack
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# qq^H*^,qq^whatever^
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# Since system and pack require arguments (rather than assuming
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# $_ when no args are given like many other perl functions),
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# this works out to do what we need.
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cmd = "system -e pack -e #{perl_qq(state, qot, hex)}"
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if state.badchars.include?(" ")
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# We already tested above to make sure that these chars are ok
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# if space isn't.
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cmd.gsub!(" ", "${IFS}")
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end
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cmd
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end
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def perl_qq(state, qot, hex)
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# Find a quoting character to use
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state.badchars.unpack('C*') { |c| qot.delete(c.chr) }
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# Throw an error if we ran out of quotes
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raise EncodingError if qot.length == 0
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sep = qot[0].chr
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# Use an explicit length for the H specifier instead of just "H*"
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# in case * is a badchar for the module, and for the case where this
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# ends up unquoted so the shell doesn't try to expand a path.
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"qq#{sep}H#{hex.length}#{sep},qq#{sep}#{hex}#{sep}"
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end
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end
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