Vulnerability identifier: #VU26291

Vulnerability risk: Low

CVSSv3.1: 7 [CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2019-17190

CWE-ID: CWE-65

Exploitation vector: Local

Exploit availability: Yes

Vulnerable software:
Avast Secure Browser
Client/Desktop applications / Web browsers

Vendor: Avast Software s.r.o.

Description

The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to software sets insecure permission to C:\ProgramData\AVAST SOFTWARE\Browser\Update\Update.ini file. This file is used during application update procedure and its permissions are replaced by the "AvastBrowserUpdate.exe" program, which runs under "NT AUTHORITY\SYSTEM" account. A local user can create a hard link from the Update.ini file to any file on the system and replace permissions of arbitrary file.

Successful exploitation of the vulnerability may allow an attacker to escalate privileges on the system.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Avast Secure Browser: 70.1.973.111 - 76.0.1659.101

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External links
http://seclists.org/fulldisclosure/2020/Mar/25
http://www.avast.com/bug-bounty-credits/en/a-tribute-to-our-security-research-community
http://sidechannel.tempestsi.com/vulnerability-in-avast-secure-browser-enables-escalation-of-privileges-on-windows-eb770d196c45

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Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.