Date: Fri, 15 Jul 2022 17:17:44 -0400
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Builder XtremeRAT v3.7 / Insecure Crypto Bypass

Discovery / credits: Malvuln (John Page aka hyp3rlinx) (c) 2022
Original source:
https://malvuln.com/advisory/7f314e798c150aedd9ce41ed39318f65_B.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Builder XtremeRAT v3.7
Vulnerability: Insecure Crypto Bypass
Description: The malware builds backdoors and requires authentication to
access the GUI using credentials stored in the "user.info" config file.
XtremeRAT doesn't properly validate saved passwords are what the user
actually set when saving them in user.info config. This can allow attackers
who can guess the first few characters the ability to pad the rest with
zeroes or whatever character they want, providing they guess the password
length. The issue it seems is in Delphi 2009, default string type changed
from ANSI, the MD5 implementation is not unicode aware generating incorrect
hashes. Therefore, a user may enter the password "abc123" thinking that is
the exact password which will grant access to the builder. However, the
flaw allows attackers the ability to more easily bypass authentication as
only part of the password will now be required as the remainder can be any
characters E.g. abc000. Moreover, the hashing implementation used makes no
use of a salt. Creating a similar password hash to logon, requires the
resulting file size should be be 64 bytes not 32. If you just copy and
paste a hash into a file you may see it is only 32 bytes, the one generated
by XtremeRAT is 64 bytes as it is encoded.
Family: Xtreme
Type: PE32
MD5: 7f314e798c150aedd9ce41ed39318f65
Vuln ID: MVID-2022-0624
Disclosure: 07/15/2022

Exploit/PoC:
import os, hashlib

#Creates broken unicode MD5 hashes to change an existing XtremeRAT config
password.
#By malvuln
#
#=================================================================================
#Basically, if the actual password is 'abc123' and was generated by
XtremeRAT
#we only need to guess 3 out of 6 chars E.g. abc000
#as long as we can guess the length we can bypass the need to know the full
password.
#We can also emulate broken passwords and replace "user.info" config with
ours.

passwd = u'abc'
tmp = hashlib.md5(passwd.encode('utf-16le'))

print("[+] XtremeRAT v3.7 ")
print("[+] Password hash bypass created")
print("[+] By malvuln")
print("[-] " +tmp.hexdigest())
print("Login using abc000 or any last three chars!")

#outputs: ce1473cf80c6b3fda8e3dfc006adc315
#HEX: 610062006300
#Login using abc000, abc!@# or abc123 it don't matter.

XRat_Config="C:\\XtremeRAT_v3.7\\user.info"

if os.path.exists(XRat_Config):
    os.remove(XRat_Config)
f=open(XRat_Config, "w", encoding='utf-16LE')
f.write(_hash2)
f.close()

Disclaimer: The information contained within this advisory is supplied
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provided that it is not altered except by reformatting it, and that due
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contained herein and accepts no responsibility for any damage caused by the
use or misuse of this information. The author prohibits any malicious use
of security related information or exploits by the author or elsewhere. Do
not attempt to download Malware samples. The author of this website takes
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handling or the downloading of ANY Malware mentioned on this website or
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