Trustwave SpiderLabs Security Advisory TWSL2017-016:
Local kernel heap buffer overflow Vulnerability in ESET DESLock+ client application

Published: 08/15/2017
Version: 1.0

Vendor: DESlock (http://www.deslock.com/)
Product: DESLock+ client
Version affected: <= 4.8.16

Product description:
DESlock+ Standard/Pro client applications provide comprehensive encryption of 
email, file & folder encryption and policy driven removable media encryption 
protection for USB flash drives and other removable storage.

Finding 1: Local kernel heap buffer overflow
*****Credit: Neil Kettle of Trustwave 
CVE: CVE-2017-12840
CWE: CWE-122

A kernel driver, namely DLMFENC.sys, bundled with the DESLock+ client 
application contains a locally exploitable heap based buffer overflow in the 
handling of an IOCTL message of type 0x0FA4204. The vulnerability is present 
due to the kernel driver failing to allocate sufficient memory on the kernel 
heap to contain a user supplied string as such the string is copied into a 
buffer of constant size (0x1000-bytes) and thus an overflow condition results. 
Access to the kernel driver is permitted through an obfuscated interface 
whereby bytes of user supplied message are ‘authenticated’ via an obfuscation 
routine employing a linear equation as follows:

static void
xor_mask_req (struct ioctl_req *req, UCHAR *xor_buf)
{
  DWORD i, pid;
  PCHAR ptr;

  pid = GetCurrentProcessId ();
  for (i = 0, ptr = (PCHAR) req; i < 0x0C; i++, ptr++)
    *ptr ^= xor_buf[i & 0x0F] ^ pid;
}

The contents of ‘xor_buf’ are obtained from the kernel driver and are set as 
the obfuscated output of a call to KeQueryPerformanceCounter. Exploitation of 
the issue is possible locally and yields arbitrary code code execution with 
ring 0 privileges.

Remediation Steps:
Fixes for this vulnerability were released in DESLock+ client 4.8.17. Please note 
that Trustwave SpiderLabs have not verified this fix.

Revision History:
05/30/2017 - Vulnerability disclosed
08/03/2017 - Patch released by vendor
08/15/2017 - Advisory published

References
1. https://www.deslock.com/downloads.php


About Trustwave:
Trustwave is the leading provider of on-demand and subscription-based
information security and payment card industry compliance management
solutions to businesses and government entities throughout the world. For
organizations faced with today's challenging data security and compliance
environment, Trustwave provides a unique approach with comprehensive
solutions that include its flagship TrustKeeper compliance management
software and other proprietary security solutions. Trustwave has helped
thousands of organizations--ranging from Fortune 500 businesses and large
financial institutions to small and medium-sized retailers--manage
compliance and secure their network infrastructure, data communications and
critical information assets. Trustwave is headquartered in Chicago with
offices throughout North America, South America, Europe, Africa, China and
Australia. For more information, visit https://www.trustwave.com

About Trustwave SpiderLabs:
SpiderLabs(R) is the advanced security team at Trustwave focused on
application security, incident response, penetration testing, physical
security and security research. The team has performed over a thousand
incident investigations, thousands of penetration tests and hundreds of
application security tests globally. In addition, the SpiderLabs Research
team provides intelligence through bleeding-edge research and proof of
concept tool development to enhance Trustwave's products and services.
https://www.trustwave.com/spiderlabs

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