CVE-2019-17190 Information

Description

A Local Privilege Escalation issue was discovered in Avast Secure Browser 76.0.1659.101. The vulnerability is due to an insecure ACL set by the AvastBrowserUpdate.exe (which is running as NT AUTHORITY\SYSTEM) when AvastSecureBrowser.exe checks for new updates. When the update check is triggered the elevated process cleans the ACL of the Update.ini file in PROGRAMDATA\Avast Software\Browser\Update\ and sets all privileges to group Everyone. Because any low-privileged user can create delete or modify the Update.ini file stored in this location an attacker with low privileges can create a hard link named Update.ini in this folder and make it point to a file writable by NT AUTHORITY\SYSTEM. Once AvastBrowserUpdate.exe is triggered by the update check functionality the DACL is set to a misconfigured value on the crafted Update.ini and consequently to the target file that was previously not writable by the low-privileged attacker.

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Reference

http://packetstormsecurity.com/files/156844/Avast-Secure-Browser-76.0.1659.101-Local-Privilege-Escalation.html http://seclists.org/fulldisclosure/2020/Mar/25 https://www.avast.com/bug-bounty-credits/en/a-tribute-to-our-security-research-community

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

HIGH

Availability Impact

HIGH

Base Score

HIGH

Base Severity

7.8