Kerio Technologies Kerio Personal Firewall and Kerio Server
         Firewall FWDRV driver
  Local denial of service
  by Piotr Bania <bania.piotr@gmail.com>
  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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