Avast sandbox escape via arbitrary file write in virtualized environment

Overview

Insufficient isolation in the Avast sandbox file virtualization layer on Windows allows a local, low-privileged attacker executing inside the sandbox to write arbitrary files outside sandbox containment and execute code on the host.

The sandbox virtualizes file system operations by intercepting write requests to protected system directories. However, the virtualization implementation fails to properly validate write targets in certain edge cases, allowing writes to bypass the virtualization redirection and reach the actual host file system in protected locations.

An attacker can exploit this to overwrite executable files, system libraries, or startup configurations with arbitrary content, leading to code execution with host privileges on subsequent system operations or reboot.

Affected

• avast_antivirus_avast_one_avast_premium_security_avast_ultimate < 26.7
• avg_antivirus_free_avg_internet_security_avg_ultimate < 26.7
• norton_antivirus_plus_norton_360_standard_norton_360_deluxe_norton_360_advanced < 26.7

Remediation

Gen Digital has released a fix in Avast, AVG, and Norton version 26.7 and later. The fix improves validation in the file virtualization layer to correctly identify protected directories and enforce write redirection in all code paths, preventing bypass of sandbox file isolation.

Upgrade to version 26.7 or later to remediate this issue.