CVE-2025-3500 Overview
CVE-2025-3500 is a critical Integer Overflow or Wraparound vulnerability (CWE-190) affecting Avast Antivirus on Windows systems. This vulnerability allows attackers to achieve Privilege Escalation by exploiting improper handling of integer values within the antivirus software. With a CVSS score of 9.0 (Critical), this vulnerability poses a significant risk to organizations relying on Avast Antivirus for endpoint protection.
The vulnerability exists in Avast Antivirus versions starting from 25.1.981.6 and is resolved in version 25.3. The network-based attack vector combined with the potential for complete system compromise makes this a high-priority security issue requiring immediate attention.
Critical Impact
This integer overflow vulnerability enables attackers to escalate privileges on affected Windows systems, potentially gaining elevated access to execute arbitrary code with system-level permissions. The CVSS:3.1 vector (AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H) indicates high impact on confidentiality, integrity, and availability with a changed scope, meaning the vulnerable component can affect resources beyond its security scope.
Affected Products
- Avast Antivirus for Windows version 25.1.981.6
- Avast Antivirus for Windows versions between 25.1.981.6 and 25.3
Discovery Timeline
- December 1, 2025 - CVE-2025-3500 published to NVD
- December 2, 2025 - Last updated in NVD database
Technical Details for CVE-2025-3500
Vulnerability Analysis
The vulnerability is classified as an Integer Overflow or Wraparound (CWE-190), which occurs when an arithmetic operation attempts to create a numeric value that exceeds the range that can be represented within the allocated storage space. In the context of Avast Antivirus, this integer overflow condition can be exploited to bypass security controls and escalate privileges.
Integer overflow vulnerabilities in security software are particularly dangerous because antivirus products typically operate with elevated system privileges. When an attacker successfully triggers an integer overflow, they may be able to:
- Corrupt memory structures used for access control decisions
- Bypass bounds checking mechanisms
- Overwrite critical security metadata
- Gain control over privileged execution contexts
The CVSS vector CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H indicates that while the attack can be initiated remotely over the network with low complexity, it requires low privileges and some user interaction. The "Changed" scope (S:C) is particularly concerning as it means successful exploitation can impact components outside the vulnerable software's security authority.
Root Cause
The root cause of CVE-2025-3500 lies in improper validation of integer arithmetic operations within Avast Antivirus. When processing certain inputs, the application fails to adequately verify that calculated values remain within acceptable bounds before using them in security-sensitive operations. This oversight allows attackers to craft malicious inputs that cause integer values to wrap around, leading to unexpected behavior in privilege management routines.
Integer overflow vulnerabilities typically arise from:
- Missing bounds validation before arithmetic operations
- Implicit type conversions between signed and unsigned integers
- Incorrect assumptions about maximum input sizes
- Failure to use safe integer arithmetic libraries
Attack Vector
The attack vector for CVE-2025-3500 is network-based, meaning an attacker can potentially exploit this vulnerability remotely. The exploitation path involves:
- Initial Access: The attacker requires low-level privileges on the target system and must interact with the victim in some capacity (user interaction required)
- Triggering the Overflow: Crafted input is delivered to the Avast Antivirus component that contains the vulnerable integer handling code
- Memory Corruption: The integer overflow causes memory allocation or access control calculations to produce incorrect values
- Privilege Escalation: The corrupted state is leveraged to elevate privileges beyond the attacker's original access level
The EPSS (Exploit Prediction Scoring System) data indicates a 0.025% probability of exploitation, placing this vulnerability in the 6.173 percentile. While no public exploits are currently available, the critical severity and privilege escalation potential warrant proactive remediation.
Detection Methods for CVE-2025-3500
Indicators of Compromise
- Unusual process behavior from Avast Antivirus services running with unexpected elevated privileges
- Anomalous memory allocation patterns in Avast-related processes
- System event logs showing privilege escalation attempts originating from antivirus components
- Unexpected child processes spawned by Avast Antivirus with elevated privileges
Detection Strategies
Organizations should implement multi-layered detection to identify potential exploitation attempts:
Endpoint Detection: Monitor for anomalous behavior in Avast Antivirus processes, particularly unexpected privilege changes or memory access violations. SentinelOne's behavioral AI can detect exploitation attempts by identifying deviation from normal antivirus software behavior patterns.
Process Monitoring: Watch for unusual parent-child process relationships where Avast processes spawn unexpected elevated processes. This can indicate successful privilege escalation.
Memory Analysis: Implement runtime memory protection to detect integer overflow conditions that lead to heap or stack corruption in monitored processes.
Version Auditing: Regularly scan endpoints to identify systems running vulnerable Avast Antivirus versions (25.1.981.6 to versions before 25.3).
Monitoring Recommendations
Security teams should configure the following monitoring capabilities:
- Enable verbose logging for Avast Antivirus services
- Monitor Windows Security Event logs (Event IDs 4624, 4672, 4688) for privilege-related anomalies
- Implement file integrity monitoring on Avast Antivirus installation directories
- Deploy endpoint detection solutions capable of identifying integer overflow exploitation patterns
- Set up alerts for unexpected service account privilege changes
How to Mitigate CVE-2025-3500
Immediate Actions Required
- Update Avast Antivirus to version 25.3 or later immediately on all affected Windows systems
- Conduct an inventory of all endpoints running Avast Antivirus to identify vulnerable versions
- Implement network segmentation to limit the attack surface for systems pending updates
- Enable enhanced monitoring on endpoints running vulnerable versions until patched
- Review system logs for any indicators of prior exploitation attempts
Patch Information
Gen Digital, the parent company of Avast, has released a security update addressing CVE-2025-3500. Organizations should upgrade to Avast Antivirus version 25.3 or later to remediate this vulnerability.
For detailed patch information and security advisories, consult the official Gen Digital security advisory page at: https://www.gendigital.com/us/en/contact-us/security-advisories/
Ensure automatic updates are enabled for Avast Antivirus to receive future security patches promptly. For enterprise deployments, coordinate with your Avast management console to push updates across the organization.
Workarounds
If immediate patching is not feasible, consider the following temporary mitigations:
- Restrict network access to affected systems where possible to reduce the attack surface
- Implement application whitelisting to limit what processes can execute with elevated privileges
- Enable additional endpoint protection controls to monitor for privilege escalation attempts
- Consider temporarily deploying alternative endpoint protection while planning the upgrade path
- Apply the principle of least privilege to all user accounts to minimize the impact of potential exploitation
# Verify Avast Antivirus version on Windows (PowerShell)
Get-ItemProperty "HKLM:\SOFTWARE\AVAST Software\Avast" | Select-Object -Property Version
# Check for vulnerable versions in enterprise environments
# Versions between 25.1.981.6 and 25.3 require immediate update
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
