CVE-2026-80302 in AVG Antivirus Free
Summary
by MITRE • 11/06/2026
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.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/06/2026
The vulnerability identified as an insufficient isolation flaw within the Avast sandbox environment represents a critical failure in boundary enforcement mechanisms designed to contain potentially malicious software. This security component operates by virtualizing file system interactions for processes running inside the isolated container, specifically intercepting write requests directed at protected system directories on Windows operating systems. The fundamental design intent is to ensure that any modifications made by untrusted code remain confined within a temporary, disposable layer that does not persist or affect the underlying host environment upon termination of the sandboxed process. However, the implementation contains logical errors in how it validates and redirects these write targets under specific edge cases, creating a pathway for data exfiltration and privilege escalation beyond the intended containment perimeter.
From a technical perspective, the core issue lies in the failure to properly validate write destinations during certain file system operations. When an application inside the sandbox attempts to modify files located in protected areas such as Program Files or Windows System directories, the virtualization layer is supposed to redirect these writes to a private shadow copy within the sandbox environment. Due to inadequate validation logic, there are scenarios where this redirection mechanism fails, allowing write requests to bypass the virtualization layer entirely and interact directly with the actual host file system. This breakdown in isolation means that operations intended for the isolated container effectively become direct modifications to the host machine's critical directories, circumventing standard access controls and security boundaries established by the operating system and the antivirus software itself.
The operational impact of this vulnerability is severe, as it enables a local attacker with low privileges inside the sandbox to achieve arbitrary code execution on the host system. By exploiting the file write bypass, an adversary can overwrite executable files, replace legitimate system libraries, or modify startup configurations such as registry keys associated with auto-start programs. These modifications persist beyond the lifecycle of the sandboxed process because they are written directly to the persistent host storage rather than a temporary virtualized layer. Consequently, when the host machine performs subsequent operations that load these compromised binaries or executes scripts from modified configuration files, the malicious code runs with the privileges of the user account associated with those system processes, effectively granting the attacker full control over the underlying operating environment without requiring additional exploitation steps to escalate privileges through other means.
This vulnerability aligns closely with CWE-250, which describes execution with unnecessary privileges, and CWE-78, pertaining to improper neutralization of special elements used in an OS command, as it involves manipulating system files to alter behavior. In the context of the MITRE ATT&CK framework, this flaw facilitates techniques related to Defense Evasion by bypassing file virtualization protections and Persistence through modification of startup items or registry run keys. The ability to write arbitrary content outside sandbox containment effectively neutralizes one of the primary defensive layers provided by endpoint protection suites that rely on behavioral analysis within sandboxes for detecting unknown threats.
Mitigation strategies must focus on addressing both immediate remediation and long-term architectural improvements. Users should immediately update Avast software to versions where this validation logic has been corrected, ensuring that file system interception rules are strictly enforced without exception for the identified edge cases. Security administrators should monitor for unusual modifications in protected system directories, particularly those occurring shortly after sandboxed applications have executed, as these may indicate exploitation attempts. Furthermore, implementing strict application control policies and least-privilege access models can limit the potential impact if such a vulnerability is present but not yet patched, reducing the likelihood that an attacker can successfully overwrite critical executables or libraries to achieve persistent host-level code execution.