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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