Major Flaw in Avast Free Antivirus Exposes Users to High-Level System Attacks
A critical bug buried deep within Avast’s Free Antivirus software has raised red flags across the cybersecurity landscape. Researchers recently uncovered a vulnerability that, if left unpatched, could hand over full system control to attackers—enabling them to run malicious code with kernel-level privileges.
Designated CVE-2025-3500, this flaw received a CVSS score of 8.8, indicating its high severity. Avast patched the issue promptly, and the details were disclosed publicly on April 24, 2025.
At the center of the problem is the aswbidsdriver kernel module, part of Avast’s free antivirus engine. The vulnerability stems from flawed input handling—specifically, a failure to properly validate user-controlled data. The result? An integer overflow that occurs before memory is allocated, opening the door to privilege escalation and remote code execution at the most trusted level of the system: the kernel.
The Zero Day Initiative (ZDI), which issued the advisory, explains: “Local attackers can exploit this flaw to elevate their permissions and run arbitrary commands. However, they must already have a foothold on the machine with basic access to trigger it.”
While the exploit requires local access—meaning attackers can’t use it remotely without first breaching the system—the risk is far from trivial. Once inside, bad actors could effectively take full command of the affected device.
Security researcher Baris Akkaya discovered the flaw and reported it to Avast on April 2, 2025. Avast’s response was swift: a patch was rolled out in version 25.3.9983.922, and users are strongly advised to update immediately.
The vulnerability impacts multiple editions of Avast Free Antivirus, with affected versions dating as far back as 20.1.2397 through 2016.11.1.2262, according to the Cybersecurity Help database.
Unfortunately, this isn’t Avast’s first brush with software weaknesses. In recent years, similar issues have been documented in other Avast offerings like Cleanup Premium and Premium Security—raising ongoing questions about secure development practices across the suite.
To reduce exposure to such threats, security professionals strongly advise enabling automatic updates and using non-admin user accounts for daily computing—proven practices that limit the blast radius of privilege escalation attacks.
With hundreds of millions of users worldwide, Avast Free Antivirus is a cornerstone of home digital defense. That makes this bug not just a technical issue, but a critical wake-up call for anyone depending on free tools to stay safe in an increasingly hostile cyber world.
