SIG^2 Vulnerability Research Advisory
Prevx Home v1.0 Instrusion Prevention Features Can Be Disabled by Direct
Service Table Restoration
by Tan Chew Keong
Release Date: 22 Nov 2004
ADVISORY URL
http://www.security.org.sg/vuln/prevxhome.html
SUMMARY
Prevx Home (https://www.prevx.com) is a state-of-the-art Host Intrusion
Prevention Software that is designed to protect the user against the next Zero
Day Hacker attacks, Internet Worms and Spyware Installation without expecting
the user to perform constant updates to their system.
Prevx Home's registry and buffer overflow protection features are implemented
by hooking several native APIs in kernel-space by modifying entries within the
SDT ServiceTable. This means that a malicious program with Administrator
privilege can disable these features by restoring the running kernel's SDT
ServiceTable with direct writes to \device\physicalmemory.
TESTED SYSTEM
Prevx Home Version 1.0 Build 2.1.0.0 on WinXP SP0, SP2.
DETAILS
Prevx Home prevents malicious code from modifying critical Windows registry
keys by prompting the user for action whenever such an attempt is detected.
Examples of protected registry keys include the Run-key and Internet Explorer's
registry settings. Prevx Home can also protect the system against buffer
overflow exploits.
Prevx Home's registry and buffer overflow protection feature is implemented by
hooking several native APIs in kernel-space by modifying entries within the SDT
ServiceTable. Hooking is performed by Prevx Home's kernel driver that replaces
several entries within the SDT ServiceTable.
It is possible to disable Prevx Home's registry and buffer overflow protection
by restoring the running kernel's SDT ServiceTable to its original state with
direct writes to \device\physicalmemory. Restoring the running kernel's SDT
ServiceTable will effectively disable the protection offered by Prevx Home. In
other words, the registry keys that were protected by Prevx Home can now be
modified
PATCH
Upgrade to Version 2.0, which can protect against such exploits.
WORKAROUNDS
Do not run untrusted programs as Administrator.
PROOF-OF-CONCEPT
http://www.security.org.sg/vuln/prevxhome.html
DISCLOSURE TIMELINE
05 Sep 04 - Vulnerability Discovered
06 Sep 04 - Initial Vendor Notification (incident number 1786)
06 Sep 04 - Initial Vendor Response
14 Sep 04 - Second Vendor Response
23 Sep 04 - Third Vendor Response
09 Nov 04 - Received Notification that Version 2.0, which can protect against
such exploits, has been released
22 Nov 04 - Public Release
GREETINGS
All guys at SIG^2 G-TEC Lab
http://www.security.org.sg/webdocs/g-tec.html
"IT Security...the Gathering. By enthusiasts for enthusiasts."
