Auth bypass in Avast Secure Browser
CVE-2019-17190
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.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.005 (42.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 42.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Avast Secure Browser — versions 76.0.1659.101
Weakness classification (CWE)
Public proof-of-concept exploits
References
- www.avast.com/bug-bounty-credits/en/a-tribute-to-our-security-research-community (Vendor Advisory)
- seclists.org/fulldisclosure/2020/Mar/25 (mailing-list, Mailing List, Third Party Advisory)
- packetstormsecurity.com/files/156844/Avast-Secure-Browser-76.0.1659.101-Local-P… (VDB Entry, Third Party Advisory)
Frequently asked questions
- What is CVE-2019-17190?
- CVE-2019-17190 is a high-severity vulnerability in Avast Secure Browser, classified under Incorrect Authorization. CVSS score: 7.8/10. Published 2020-01-27.
- How severe is CVE-2019-17190?
- High severity. CVSS v3 base score is 7.8 out of 10.
- Is CVE-2019-17190 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.