Security researchers have revealed a critical vulnerability in Avast Free Antivirus that could allow attackers to gain elevated system privileges and execute malicious code with kernel-level access.
The vulnerability, tracked as CVE-2025-3500, received a high CVSS score of 8.8 and was made public on April 24, 2025, after Avast issued a patch.
Technical Details of the Vulnerability
The security flaw resides in the Avast Free Antivirus aswbidsdriver kernel driver and is caused by incorrect validation of user-supplied data.
According to the advisory published by the Zero Day Initiative (ZDI), this validation issue can cause an integer overflow before a buffer is allocated. Once exploited, this vulnerability allows attackers to escalate privileges and execute arbitrary code with kernel-level permissions.
Impact and Operational Requirements
The local nature of the exploit means that an attacker must first gain the ability to execute low-privileged code on the target system in order to exploit the vulnerability. Although this limits the immediate threat, the consequences can be severe if a system is already compromised, as the attacker would gain full control over the affected device.
Patch and Mitigation
Cybersecurity expert Baris Akkaya discovered and reported the vulnerability to Avast on April 2, 2025. The company responded quickly, releasing a fix in version 25.3.9983.922, which is strongly recommended to be installed immediately.
The vulnerability affects multiple versions of Avast Free Antivirus, with the Cybersecurity Help database listing affected versions from 20.1.2397 to 2016.11.1.2262. Users running these versions should update their software as soon as possible.
Security Recommendations
- Automatic Updates: Enable automatic updates for antivirus software to ensure you receive critical security patches in a timely manner.
- Principle of Least Privilege: Use standard user accounts for daily activities instead of accounts with administrator privileges. This can mitigate the impact of similar vulnerabilities.
Conclusion
Given that Avast Free Antivirus is one of the most popular antivirus solutions globally, with hundreds of millions of installations, this vulnerability is particularly concerning for home users. It is crucial that users install the patch provided by Avast to protect against this escalation of privileges that allows full control of the system.
References
- Vulnerability: CVE-2025-3500
- Advisory Source: Zero Day Initiative (ZDI)
- Patch Version: Avast Free Antivirus 25.3.9983.922