Insufficient isolation in Avast's sandbox file virtualization layer on Windows permits a local, low‑privileged user running inside the sandbox to write arbitrary files outside the containment zone; the virtualization mechanism fails to validate certain write targets, enabling overwriting of executable binaries, system libraries, or startup configurations. This can lead to malicious code execution with full host privileges after a reboot or subsequent system operation.

The flaw affects Gen Digital’s AVG Antivirus Free, AVG Internet Security, AVG Ultimate, Avast Antivirus, Avast One, Avast Premium Security, Avast Ultimate, and the Norton suite (Norton Antivirus Plus, Norton 360 Standard, Norton 360 Deluxe, Norton 360 Advanced) on Windows. Versions prior to 26.7 are vulnerable, and the vendor has released a patch in version 26.7 and later for all affected Avast, AVG, and Norton products.

The attack requires only local, low‑privileged access to the sandboxed process, a condition achievable by any user executing content that triggers the sandbox. While public EPSS data are unavailable, the vulnerability is a classic CWE‑434 input validation flaw combined with CWE‑653 improper file‑name validation, which permits direct host‑level execution. The impact is host‑wide code execution, demanding high‑urgency remediation even though the vulnerability is local.