CVE-2025-4134
📋 TL;DR
A local user can spoof or tamper with Avast Business Antivirus update files due to insufficient file validation in the do_update_vps function. This vulnerability affects Avast Business Antivirus for Linux version 4.5 running on Linux systems, allowing attackers with local access to potentially compromise the antivirus update mechanism.
💻 Affected Systems
- Avast Business Antivirus for Linux
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
An attacker could replace legitimate update files with malicious ones, potentially leading to antivirus bypass, system compromise, or malware installation through the trusted update channel.
Likely Case
Local privilege escalation or antivirus evasion by tampering with update files to disable or weaken protection mechanisms.
If Mitigated
Limited impact if proper file permissions restrict write access to update directories and integrity checks are implemented.
🎯 Exploit Status
Exploitation requires local access to the system. The vulnerability involves file write operations that lack proper validation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: https://www.gendigital.com/us/en/contact-us/security-advisories/
Restart Required: No
Instructions:
Check the vendor advisory for patch availability. If available, update to the patched version through the standard update mechanism.
🔧 Temporary Workarounds
Restrict File Permissions
linuxLimit write access to Avast update directories to prevent unauthorized file modifications.
chmod 755 /opt/avast/update
chown root:root /opt/avast/update
Monitor Update Files
linuxImplement file integrity monitoring on Avast update directories to detect unauthorized changes.
auditctl -w /opt/avast/update -p wa -k avast_update
🧯 If You Can't Patch
- Implement strict access controls to limit local user privileges on affected systems.
- Deploy additional security monitoring to detect unauthorized file modifications in Avast directories.
🔍 How to Verify
Check if Vulnerable:
Check if Avast Business Antivirus version 4.5 is installed: dpkg -l | grep avast or rpm -qa | grep avastCheck Version:
avast --version or check /opt/avast/version.txtVerify Fix Applied:
Verify the installed version is newer than 4.5 after applying vendor updates.📡 Detection & Monitoring
Log Indicators:
- Unauthorized file writes to Avast update directories
- Failed integrity checks on update files
- Unexpected process execution from Avast update locations
Network Indicators:
- Unusual outbound connections from Avast processes following local file modifications
SIEM Query:
source="avast" AND (event_type="file_write" AND file_path="/opt/avast/update/*") OR (process_execution AND parent_process="avast" AND process_path="/opt/avast/update/*")