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ZoneAlarm TrueVector Internet Monitor service insecure NTFS permissions  
vulnerability  
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Yorick Koster, December 2019  
  
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Abstract  
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A vulnerability was found in the TrueVector Internet Monitor service,  
which is installed as part of the Check Point ZoneAlarm firewall. This  
vulnerability allows a local attacker to cause the affected service to  
change the file permissions of arbitrary local files. After the file  
permissions have been changed, the attacker can then overwrite its  
content, and ultimately gain elevated privileges on the vulnerable  
machine.  
  
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Tested version  
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This vulnerability was successfully verified on ZoneAlarm Free Firewall  
v15.8.023.18219/TrueVector Internet Monitor v15.8.7.18219.  
  
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Fix  
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Check Point released new versions of ZoneAlarm Firewall that fix this  
vulnerability. The latest version of ZoneAlarm Free Firewall  
(v15.8.043.18324) can be obtained from  
https://www.zonealarm.com/software/free-firewall/download.  
  
The 2020-03 Cumulative Update [2] for Windows 10 adds hardlink  
mitigations. After installing this update, Windows will require write  
access on the target file otherwise the hardlink won't be created.  
Requiring write access on the target file also mitigates this issue.  
  
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Introduction  
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A vulnerability was found in the TrueVector Internet Monitor service,  
which is installed as part of the Check Point ZoneAlarm firewall. This  
vulnerability allows a local attacker to cause the affected service to  
change the file permissions of arbitrary local files. After the file  
permissions have been changed, the attacker can then overwrite its  
content, and ultimately gain elevated privileges on the vulnerable  
machine.  
  
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Vulnerability details  
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The TrueVector Internet Monitor service is running as LocalSystem, it  
periodically creates a number of backup files within the  
%ProgramData%\CheckPoint\ZoneAlarm\Data\ folder. When these files are  
created, their file permissions are explicitly set to Full Control for  
Authenticated Users. A local attacker can create a hardlink with the  
same name as the backup files, causing the permissions of another file  
to be changed.  
  
After the file permissions have been changed, the attacker can then  
overwrite its content, and ultimately gain elevated privileges on the  
vulnerable machine. Hardlinks can be created using James Forshaw's [3]  
CreateHardlink [4] tool.  
  
CreateHardlink.exe  
"%ProgramData%\CheckPoint\ZoneAlarm\Data\bu_tosave.ndb"  
"%SystemRoot%\win.ini"  
CreateHardlink.exe  
"%ProgramData%\CheckPoint\ZoneAlarm\Data\bu_todelete.ndb"  
"%SystemRoot%\win.ini"  
  
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References  
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[1] https://www.securify.nl/advisory/SFY20200317/zonealarm-truevector-internet-monitor-service-insecure-ntfs-permissions-vulnerability.html  
[2] https://www.catalog.update.microsoft.com/Search.aspx?q=KB4540673  
[3] https://twitter.com/tiraniddo  
[4] https://github.com/googleprojectzero/symboliclink-testing-tools/tree/master/CreateHardlink