Kerio Personal Firewall and Kerio Server Firewall FWDRV driver Local Denial of Service

Advisory Content :

Kerio Technologies Kerio Personal Firewall and Kerio Server
Firewall FWDRV driver
Local denial of service
by Piotr Bania <bania.piotr (at) gmail (dot) com [email concealed]>
http://pb.specialised.info

Original location:
http://pb.specialised.info/all/adv/kerio-fwdrv-dos-adv.txt

Severity: Low (local machine denial of service -
BSOD)

Software affected: Tested on Kerio Personal Firewall 4
(4.2.0) and KerioServerFirewall
version 1.1.1, however it is highly

possible that earlier versions
are also vulnerable.

I. BACKGROUND

From kerio.com website:

"Kerio Personal Firewall represents smart, easy-to-use personal
security technology that fully protects personal computers
against hackers and internal misuse"

"Kerio ServerFirewall offers IT and security administrators a
powerful and easy-to-use tool to protect their server systems
from worms, buffer-overflow and other internet security
threats."

II. DESCRIPTION

FWDRV driver (core part of the firewall system) monitors all
programs that are trying to connect to the internet. While doing
necessary checks, FWDRV parses the Process Environment Block
(PEB) like the code shows:

;----------SNIP--------------------------------------------
.text:0041C04E mov ecx, [ebp+var_4] ; ECX = PEB base
.text:0041C051 mov edx, [ecx+0Ch] ; EDX = PEB_LDR_DATA
;----------SNIP--------------------------------------------

However while parsing the PEB FWDRV doesn't check if the memory
with Process Environment Block is accessible. It means that if
attacker will set PAGE_NOACCESS or PAGE_GUARD protection to the
PEB block the FWDRV will cause an fatal exception and the
machine will crash.

III. IMPACT

Sample scenario:
Executing connect api function with previously PAGE_NOACCESS
protection set to Process Environment Block will cause an local
machine crash.

IV. POC CODE

Sample POC code was released to vendor.

best regards,
Piotr Bania

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Kerio Personal Firewall and Kerio Server Firewall FWDRV driver Local Denial of Service