Critical Alert: Integer Overflow in Avast Antivirus Leads to Privilege Escalation (CVE-2025-3500)

Overview

A critical security vulnerability, identified as CVE-2025-3500, has been discovered in Avast Antivirus version 25.1.981.6 running on Windows operating systems. This vulnerability, stemming from an integer overflow or wraparound, could allow an attacker to escalate their privileges to a higher level, potentially gaining control of the affected system. The vulnerability affects Avast Antivirus versions from 25.1.981.6 before version 25.3.

Technical Details

The vulnerability resides in how Avast Antivirus handles certain input sizes. Specifically, an integer overflow occurs when the size of a data structure is incorrectly calculated. When this overflow happens, it allows an attacker to write outside the bounds of an allocated buffer, potentially overwriting critical system data. This leads to privilege escalation because an attacker can leverage this out-of-bounds write to execute arbitrary code with elevated permissions. Exploitation requires a specially crafted input that triggers the integer overflow condition within the vulnerable Avast Antivirus component. The specific component vulnerable is not publicly known at this time, and we do not recommend that you try to reverse engineer this vulnerability.

CVSS Analysis

This vulnerability has been assigned a CVSS score of 9, indicating its critical severity. A CVSS score of 9 signifies that the vulnerability is easily exploitable, requires minimal user interaction, and could lead to significant damage, including complete system compromise.

Possible Impact

The successful exploitation of CVE-2025-3500 can have severe consequences:

• Privilege Escalation: An attacker can gain administrative or system-level privileges, allowing them to perform any action on the affected system.
• Malware Installation: Attackers can install malware, including ransomware, keyloggers, and other malicious software.
• Data Theft: Sensitive data can be stolen, including passwords, financial information, and personal files.
• System Compromise: The entire system can be compromised, potentially leading to data loss, system instability, and denial of service.
• Lateral Movement: In a networked environment, a compromised system can be used as a stepping stone to attack other systems on the network.

Mitigation and Patch Steps

The recommended mitigation is to immediately update Avast Antivirus to version 25.3 or later. Follow these steps:

1. Open Avast Antivirus.
2. Go to Menu > Settings > Update.
3. Click on Update to check for and install the latest version.
4. Restart your computer after the update is complete.

If automatic updates are enabled, the update should be applied automatically. However, it’s always a good practice to verify that you are running the latest version.

References

• Gen Digital Security Advisory
• NIST NVD CVE-2025-3500 (When available)