Avira Internet Security Vulnerabilities: Deserialize, Delete, and Escalate
Antivirus software is designed to protect users from cyber threats, but when vulnerabilities exist within these tools, they can ironically become powerful attack vectors. Recent research by Quarkslab uncovered three critical flaws in Avira Internet Security, exposing users to risks of privilege escalation, arbitrary file deletion, and insecure deserialization.
Key Vulnerabilities in Avira Internet Security
1. Arbitrary File Deletion (CVE-2026-27748)
- Found in the Software Updater module.
- Attackers can exploit this flaw to delete arbitrary files.
- Impact: Privilege escalation and potential system destabilization.
2. Insecure Deserialization (CVE-2026-27749)
- Located in the System Speedup component.
- Uses unsafe .NET BinaryFormatter for deserialization.
- Impact: Malicious payloads can be executed with SYSTEM-level privileges.
3. TOCTOU Folder Deletion (CVE-2026-27750)
- Present in the Optimizer module.
- Exploits a race condition (Time-of-Check vs. Time-of-Use).
- Impact: Attackers can delete arbitrary directories with SYSTEM privileges.
Why These Flaws Matter
- High Privilege Execution: Antivirus software runs with elevated rights, making exploitation extremely dangerous.
- Privilege Escalation: Attackers can move from low-level user accounts to full SYSTEM access.
- Real-World Risk: Malware could leverage these flaws to disable security tools, gain persistence, or spread across networks.
Vulnerability Overview
| CVE ID | Component | Type of Vulnerability | Impact |
|---|---|---|---|
| CVE-2026-27748 | Software Updater | Arbitrary file delete | Privilege escalation, system damage |
| CVE-2026-27749 | System Speedup | Insecure deserialization | Arbitrary code execution as SYSTEM |
| CVE-2026-27750 | Optimizer | TOCTOU folder delete | Privilege escalation, directory removal |
Security Recommendations
- Update Immediately: Ensure Avira Internet Security is patched to the latest version.
- Monitor CVE Advisories: Track CVE-2026-27748, CVE-2026-27749, and CVE-2026-27750 for vendor updates.
- Harden Systems: Limit local user privileges and monitor for suspicious file deletions or deserialization attempts.
- Follow Best Practices: Avoid unsafe serialization methods like BinaryFormatter in .NET and validate privileged operations.
Indicators of Compromise (IOCs)
File & Process Artifacts
- Unexpected deletions of system files in
C:\Windows\System32\or security-related directories. - Abnormal activity from Avira processes (
avira.service.exe,avira.optimizer.exe,avira.updater.exe) performing file deletions outside their normal scope. - Creation of suspicious serialized payloads (
.bin,.dat,.ser) in temporary folders (%TEMP%,%APPDATA%) that are later accessed by Avira components. - Race condition exploitation traces: rapid folder creation/deletion in logs, especially targeting privileged directories.
Registry & Event Logs
- Registry changes granting SYSTEM-level privileges to non-admin accounts.
- Windows Event ID anomalies:
- Event ID 4663 (Object Access) showing Avira processes deleting protected files.
- Event ID 4688 (Process Creation) with Avira components spawning unexpected child processes.
SOC Detection Strategies
1. File Deletion Monitoring
- Rule: Alert if Avira Updater (
avira.updater.exe) deletes files outsideC:\Program Files\Avira\. - Detection Source: Sysmon Event ID 23 (File Delete).
- IOC Match: Deletion of critical OS files or AV-related executables.
2. Insecure Deserialization Exploits
- Rule: Detect execution of
.NET BinaryFormatterdeserialization from untrusted sources. - Detection Source: Sysmon Event ID 1 (Process Creation) + command-line arguments containing
BinaryFormatter.Deserialize. - IOC Match: Serialized payloads in
%TEMP%accessed by Avira System Speedup.
3. TOCTOU Exploitation
- Rule: Alert on rapid folder creation/deletion cycles initiated by
avira.optimizer.exe. - Detection Source: File system monitoring with Sysmon Event ID 11 (File Create) + Event ID 23 (File Delete).
- IOC Match: Privileged directories being deleted within milliseconds of creation.
4. Privilege Escalation Attempts
- Rule: Detect non-admin accounts spawning SYSTEM-level processes.
- Detection Source: Windows Event ID 4672 (Special Privileges Assigned).
- IOC Match: SYSTEM privileges assigned to unexpected accounts following Avira process execution.
Takeaway
- IOCs: Look for abnormal Avira process behavior, serialized payloads, and suspicious deletions.
- SOC Detections: Monitor file system activity, deserialization attempts, and privilege escalation events tied to Avira components.
- These detections help security teams spot exploitation attempts before attackers gain SYSTEM-level control.
Conclusion
Quarkslab’s findings highlight how antivirus software can become a liability if its privileged modules aren’t properly secured. These vulnerabilities in Avira Internet Security serve as a cautionary tale for both users and developers: security tools must be hardened against exploitation, or they risk becoming the very weakness attackers exploit.
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