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suri-suspicious-vbe.lua
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suri-suspicious-vbe.lua
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--[[
#*************************************************************
# Copyright (c) 2003-2015, Emerging Threats
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
# following conditions are met:
#
# * Redistributions of source code must retain the above copyright notice, this list of conditions and the following
# disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
# following disclaimer in the documentation and/or other materials provided with the distribution.
# * Neither the name of the nor the names of its contributors may be used to endorse or promote products derived
# from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS AND ANY EXPRESS OR IMPLIED WARRANTIES,
# INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
# USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
#*************************************************************
This lua script can be run standalone and verbosely on a vbe file with
echo "run()" | lua -i <script name> <vbe file>
VBE decoding based on tool written in Pascal in http://seclists.org/fulldisclosure/2003/Sep/734 :-
program vbs_dec; { Decrypts encrypted VBScript and JScript programs }
{ Copyright (c) 09/2003 Andreas Marx / http://www.av-test.org }
Chris Wakelin
Will Metcalf
--]]
--local lz = require("zlib")
local bit = require("bit")
-- {strings to match, number of matching strings needed, simple strings, description}
susp_class = {
{"http://",1,true,"Embedded URL",0},
{"[Rr][Ee][Aa][Dd][Mm][Ee][Mm][Oo]]",1,false,"Readmemory function",0},
{"powershell",1,true,"Powershell call",0},
{"[Ss][Hh][Ee][Ll][Ll][Ee][Xx][Ee][Cc]",1,false,"ShellExecute call",0},
{"[Ww][Ss][Cc][Rr][Ii][Pp][Tt]%.[Ss][Hh][Ee][Ll][Ll]",1,false,"WScript.Shell call",0},
}
function init (args)
local needs = {}
needs["http.response_body"] = tostring(true)
return needs
end
function match_strings(a,match_set,verbose)
local rtn = 0
local n,m
local num_strings = #match_set - 4
local match_num = match_set[num_strings+1]
local plain = match_set[num_strings+2]
local desc = match_set[num_strings+3]
local fnd
for n = 1, num_strings, 1 do
m = match_set[n]
if m ~= 0 then
fnd = string.find(a,m,1,plain)
if fnd then
match_set[num_strings+4] = match_set[num_strings+4] + 1
if verbose == 1 then print("Found String " .. m .. " " .. match_set[num_strings+4] .. " of " .. match_num) end
--match_set[num_strings+4] is our counter
if match_set[num_strings+4] == match_num then
if verbose == 1 then print("Found " .. desc) end
match_set[n] = 0
rtn = 1
break
else
--Found lets zero it out so we don't check again
match_set[n] = 0
end
end
end
end
return rtn
end
function common(t,verbose)
rtn = 0
u = deobfuscate(decode_vbe(t),verbose)
if #u > 0 then
if (verbose==1) then print("Found encoded VBE section(s)") end
for l,s in pairs(susp_class) do
if (verbose==1) then print("Looking for " .. s[#s-1] .. " in decoded sections") end
if match_strings(u,s,verbose) == 1 then
rtn = 1
if (verbose == 0) then
break
end
end
end
end
return rtn
end
-- return match via table
function match(args)
local t = tostring(args["http.response_body"])
return common(t,0)
end
function run()
local f = io.open(arg[1])
local t = f:read("*all")
f:close()
if common(t,1) == 1 then print("Found Suspicious String in " .. arg[1]) end
end
function base64_d(a,force_ascii)
-- requires a to be a valid base64 string -
-- only valid chars, multiple of 4 in length - else it will crash!
-- converted from Blackhole JS version :-)
keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
b = ""
for i = 1, #a, 4 do
enc1 = keyStr:find(a:sub(i,i),1,true)-1
enc2 = keyStr:find(a:sub(i+1,i+1),1,true)-1
enc3 = keyStr:find(a:sub(i+2,i+2),1,true)-1
enc4 = keyStr:find(a:sub(i+3,i+3),1,true)-1
chr1 = bit.bor(bit.lshift(enc1,2),bit.rshift(enc2,4))
chr2 = bit.bor(bit.lshift(bit.band(enc2,15),4),bit.rshift(enc3,2))
chr3 = bit.bor(bit.lshift(bit.band(enc3,3),6),enc4)
b = b .. string.char(chr1)
if enc3 ~= 64 then b = b .. string.char(chr2) end
if enc4 ~= 64 then b = b .. string.char(chr3) end
end
if force_ascii == true and b:gsub("[%w%p%s]","") ~= "" then
return a,0
else
return b,1
end
end
D_tabs = {
{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x57,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,
0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,
0x2E,0x47,0x7A,0x56,0x42,0x6A,0x2F,0x26,0x49,0x41,0x34,0x32,0x5B,0x76,0x72,0x43,
0x38,0x39,0x70,0x45,0x68,0x71,0x4F,0x09,0x62,0x44,0x23,0x75,0x3C,0x7E,0x3E,0x5E,
0xFF,0x77,0x4A,0x61,0x5D,0x22,0x4B,0x6F,0x4E,0x3B,0x4C,0x50,0x67,0x2A,0x7D,0x74,
0x54,0x2B,0x2D,0x2C,0x30,0x6E,0x6B,0x66,0x35,0x25,0x21,0x64,0x4D,0x52,0x63,0x3F,
0x7B,0x78,0x29,0x28,0x73,0x59,0x33,0x7F,0x6D,0x55,0x53,0x7C,0x3A,0x5F,0x65,0x46,
0x58,0x31,0x69,0x6C,0x5A,0x48,0x27,0x5C,0x3D,0x24,0x79,0x37,0x60,0x51,0x20,0x36}
,
{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x7B,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F,
0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,
0x32,0x30,0x21,0x29,0x5B,0x38,0x33,0x3D,0x58,0x3A,0x35,0x65,0x39,0x5C,0x56,0x73,
0x66,0x4E,0x45,0x6B,0x62,0x59,0x78,0x5E,0x7D,0x4A,0x6D,0x71,0x3C,0x60,0x3E,0x53,
0xFF,0x42,0x27,0x48,0x72,0x75,0x31,0x37,0x4D,0x52,0x22,0x54,0x6A,0x47,0x64,0x2D,
0x20,0x7F,0x2E,0x4C,0x5D,0x7E,0x6C,0x6F,0x79,0x74,0x43,0x26,0x76,0x25,0x24,0x2B,
0x28,0x23,0x41,0x34,0x09,0x2A,0x44,0x3F,0x77,0x3B,0x55,0x69,0x61,0x63,0x50,0x67,
0x51,0x49,0x4F,0x46,0x68,0x7C,0x36,0x70,0x6E,0x7A,0x2F,0x5F,0x4B,0x5A,0x2C,0x57}
,
{0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x6E,0x0A,0x0B,0x0C,0x06,0x0E,0x0F,
0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,
0x2D,0x75,0x52,0x60,0x71,0x5E,0x49,0x5C,0x62,0x7D,0x29,0x36,0x20,0x7C,0x7A,0x7F,
0x6B,0x63,0x33,0x2B,0x68,0x51,0x66,0x76,0x31,0x64,0x54,0x43,0x3C,0x3A,0x3E,0x7E,
0xFF,0x45,0x2C,0x2A,0x74,0x27,0x37,0x44,0x79,0x59,0x2F,0x6F,0x26,0x72,0x6A,0x39,
0x7B,0x3F,0x38,0x77,0x67,0x53,0x47,0x34,0x78,0x5D,0x30,0x23,0x5A,0x5B,0x6C,0x48,
0x55,0x70,0x69,0x2E,0x4C,0x21,0x24,0x4E,0x50,0x09,0x56,0x73,0x35,0x61,0x4B,0x58,
0x3B,0x57,0x22,0x6D,0x4D,0x25,0x28,0x46,0x4A,0x32,0x41,0x3D,0x5F,0x4F,0x42,0x65}
} -- cipher tables
I_tab = {
0x00,0x02,0x01,0x00,0x02,0x01,0x02,0x01,0x01,0x02,0x01,0x02,0x00,0x01,0x02,0x01,
0x00,0x01,0x02,0x01,0x00,0x00,0x02,0x01,0x01,0x02,0x00,0x01,0x02,0x01,0x01,0x02,
0x00,0x00,0x01,0x02,0x01,0x02,0x01,0x00,0x01,0x00,0x00,0x02,0x01,0x00,0x01,0x02,
0x00,0x01,0x02,0x01,0x00,0x00,0x02,0x01,0x01,0x00,0x00,0x02,0x01,0x00,0x01,0x02
} -- cipher table selector
esc_tab = {[0x26] = 0x0a; [0x23] = 0x0d; [0x2a] = 0x3e; [0x21] = 0x3c; [0x24] = 0x40} -- escaped chars
function decode_vbe(s)
t = ""
for r in string.gmatch(s,"#@~%^[%w%+/=][%w%+/=][%w%+/=][%w%+/=][%w%+/=][%w%+/=][%w%+/=][%w%+/=].-%^#~@") do
x = base64_d(r:sub(5,12))
size = x:byte(1)+(256*x:byte(2))+(256*256*x:byte(3))+(256*256*256*x:byte(4))
p = 0;
skip = 0;
for i = 1+12, math.min(size+12,#r), 1 do
if (skip == 0) then
c = r:byte(i)
if (c < 128) then
d = D_tabs[I_tab[(p % 64)+1]+1][c+1]
if ((d == 255) and (i < #r)) then
if (esc_tab[r:byte(i+1)] ~= nil) then
t = t .. string.char(esc_tab[r:byte(i+1)])
end
skip = 1
else
t = t .. string.char(d)
end
else
t = t .. string.char(c)
end
p = p + 1
else
skip = 0
end
end
end
return t
end
function deobfuscate(a, verbose)
if verbose==1 then print("Deobfuscating : " .. a) end
recursion_count = 0
num_matches = 1
while (recursion_count < 10) and (num_matches > 0) do
num_matches = 0
recursion_count = recursion_count + 1
a,n = a:gsub('\\u00(%x%x)',function(i) return string.format("%c", "0x" .. i) end) num_matches = num_matches + n
a,n = a:gsub('\\x(%x%x)',function(i) return string.format("%c", "0x" .. i) end) num_matches = num_matches + n
a,n = a:gsub('\\([0-7][0-7][0-7])',function(i) return string.format("%c", i:sub(3,3)+(8*i:sub(2,2))+(8*8*i:sub(1,1))) end) num_matches = num_matches + n
a,n = a:gsub('[Cc][Hh][Rr][Ww]?%((%d+)%)',function(i) return string.format("\39%c\39", i % 256) end) num_matches = num_matches + n
a,n = a:gsub('(["\39]) *[%&%+] *%1','') num_matches = num_matches + n
if verbose==1 and num_matches > 0 then print("Got some matches - repeating ...") end
end
if verbose==1 then print("Deobfuscating after " .. recursion_count .. " loops got : " .. a) end
return a
end