Avira Internet Security – Multiple Local Privilege Escalation Vulnerabilities
Product Overview
Product: Avira Internet Security
Vendor: Avira Operations GmbH (Gen Digital)
Affected Platform: Microsoft Windows
Affected Components:
- Avira System Speedup RealTime Optimizer Service
- Avira Software Updater Service
- Avira Cleanup / Optimization Modules
Avira Internet Security is a Windows endpoint protection suite designed to provide malware detection, system optimization, and automated maintenance capabilities. Several background services operate with SYSTEM-level privileges in order to perform system cleanup tasks, apply updates, and optimize system performance.
Multiple vulnerabilities were identified in internal components responsible for file operations and configuration processing. These components rely on background services that interact with files stored in directories accessible to standard users.
Improper validation of file paths, unsafe handling of serialized data, and insecure deletion logic were observed within these services. Because these services run with elevated privileges, improper handling of user-controlled input may allow attackers with local access to manipulate privileged operations.
If successfully exploited, the vulnerabilities could allow a low-privileged user to perform actions normally restricted to administrators, including:
- Execution of arbitrary code with SYSTEM privileges
- Deletion of protected operating system files
- Manipulation of security application components
- Establishment of persistence on the compromised system
The issues are considered high severity because exploitation may result in full compromise of the operating system.
Vulnerability Summary Table
| CVE ID | Vulnerability Name | Product | CVSS Score | Severity | Attack Vector | Privileges Required | Exploitability | Public Exploit |
|---|---|---|---|---|---|---|---|---|
| CVE-2026-27750 | Time-of-Check Time-of-Use Directory Deletion | Avira Internet Security | 7.8 | High | Local | Low | Medium | No public exploit confirmed |
| CVE-2026-27749 | Unsafe Deserialization Leading to SYSTEM Code Execution | Avira Internet Security | 8.5 | High | Local | Low | High | Proof-of-Concept discussed |
| CVE-2026-27748 | Symbolic Link Arbitrary File Deletion | Avira Internet Security | 7.8 | High | Local | Low | Medium | No public exploit confirmed |
CVE-2026-27750 – TOCTOU Arbitrary Directory Deletion
Vulnerability Description
A race condition vulnerability was identified in the Avira cleanup and optimization component responsible for removing unused directories. The service performs automated maintenance tasks by identifying directories that appear safe to remove.
During the cleanup process, a validation step is performed to verify that the target directory belongs to a temporary or non-critical location. However, the validation occurs before the deletion operation is executed.
Because the path is not revalidated during deletion, a Time-of-Check to Time-of-Use (TOCTOU) race condition becomes possible.
A directory initially approved for deletion may be replaced by an attacker with a junction point or reparse point redirecting the path to another location. When the deletion phase executes, the redirected path is removed using SYSTEM privileges.
As a result, directories outside the intended cleanup scope may be deleted.
Affected Component
Avira Optimizer Cleanup Service running under the SYSTEM account.
Exploitation Scenario
- A local attacker creates a directory that is likely to be scanned by the optimizer service.
- The directory is detected by the service and scheduled for deletion.
- Before the deletion occurs, the attacker replaces the directory with an NTFS junction pointing to another location.
- The privileged service performs the deletion operation without validating the final path.
- The target directory referenced by the junction is deleted with SYSTEM privileges.
Security Impact
- Deletion of arbitrary directories
- Potential operating system instability
- Disruption of security software
- Privilege escalation chaining possibilities
- Local denial of service
MITRE ATT&CK Mapping
| Technique | ID | Description |
|---|---|---|
| Exploitation for Privilege Escalation | T1068 | Abuse of vulnerable privileged service |
| Hijack Execution Flow | T1574 | Abuse of filesystem redirection |
| File and Directory Manipulation | T1222 | Modification of filesystem structures |
Proof-of-Concept (Educational)
The following simplified concept demonstrates how the race condition may be abused.
mkdir C:\Temp\TestFolder
mklink /J C:\Temp\TestFolder C:\Windows\System32
If the optimizer service schedules C:\Temp\TestFolder for deletion before the link replacement occurs, the redirected location may be deleted.
This demonstration is intended only to illustrate the exploitation concept.
Detection
Behavioral Indicators
- Creation of NTFS junctions shortly before cleanup tasks execute
- Deletion of directories outside expected cleanup paths
- Unexpected file deletion activity triggered by Avira cleanup services
- Rapid directory replacement events
Log Sources
- Windows Security Event Logs
- Sysmon File Creation Events
- Sysmon File Deletion Events
- Endpoint Detection and Response telemetry
- Windows Object Access auditing
Detection Queries
Windows Event Log Query
EventID=4663 AND ObjectType="Directory"
AND ProcessName="Avira*"
Sysmon Query
EventID=11 OR EventID=23
Image contains "Avira"
TargetFilename contains "System32"
Splunk Query
index=windows
(EventCode=11 OR EventCode=23)
Image="*Avira*"
| search TargetFilename="*Windows*"
Elastic Query
process.name : "Avira*" AND
(event.action : "file_delete" OR event.action : "file_create")
Mitigation
- Upgrade to the latest version of Avira Internet Security.
- Restrict write permissions for directories used by cleanup services.
- Monitor creation of junctions and reparse points.
- Enable filesystem integrity monitoring.
Official Patch / Upgrade
https://www.avira.com/en/support-download-avira-internet-security
CVE-2026-27749 – Insecure Deserialization Leading to SYSTEM Code Execution
Vulnerability Description
A critical vulnerability was identified in the Avira System Speedup RealTime Optimizer service involving the unsafe use of serialized data.
The service processes configuration or task information stored in files located within the ProgramData directory. These files are deserialized using the .NET BinaryFormatter mechanism.
BinaryFormatter reconstructs object graphs directly from serialized data. When untrusted data is processed, malicious object payloads may trigger arbitrary code execution during deserialization.
Because the configuration file can be modified by a low-privileged user, crafted serialized objects may be injected into the file.
When the service processes the file, the malicious object is instantiated and executed under SYSTEM privileges.
Affected Component
Avira System Speedup RealTime Optimizer Service
Exploitation Scenario
- A local attacker identifies the configuration file processed by the optimizer service.
- The file is replaced with a malicious serialized object payload.
- The privileged service reads and deserializes the file.
- Code embedded in the malicious object executes during deserialization.
- The attacker gains SYSTEM-level command execution.
Security Impact
- Arbitrary command execution
- Full SYSTEM privilege escalation
- Installation of persistent malware
- Security control bypass
- Deployment of additional payloads
MITRE ATT&CK Mapping
| Technique | ID | Description |
|---|---|---|
| Exploitation for Privilege Escalation | T1068 | Abuse of vulnerable service |
| Command Execution | T1059 | Execution of attacker commands |
| Persistence via Services | T1543 | Establishment of persistent services |
Proof-of-Concept (Educational)
A malicious serialized object may contain a command execution gadget chain.
Example concept:
SerializedObject -> Deserialization -> Command Execution
A payload embedded within the serialized object may launch:
cmd.exe /c whoami > C:\Temp\poc.txt
When the service processes the malicious object, the command executes with SYSTEM privileges.
This demonstration illustrates the deserialization attack mechanism.
Detection
Behavioral Indicators
- Unexpected modification of serialized configuration files
- Suspicious activity from RealTimeOptimizer service
- Command execution triggered by Avira services
- Abnormal binary content appearing in configuration files
Log Sources
- Windows Security Event Logs
- Sysmon Process Creation Logs
- Sysmon File Write Events
- EDR Behavioral Telemetry
- .NET Runtime Execution Logs
Detection Queries
Windows Event Log Query
EventID=4688
ParentProcessName="Avira.SystemSpeedup*"
Sysmon Query
EventID=1
ParentImage contains "Avira"
Image contains "cmd.exe"
Splunk Query
index=windows EventCode=4688
ParentImage="*Avira*"
Image="*cmd.exe*"
Elastic Query
process.parent.name : "Avira*" AND
process.name : ("cmd.exe","powershell.exe")
Mitigation
- Upgrade to the patched version of Avira Internet Security.
- Restrict write access to configuration files located in
ProgramData. - Monitor deserialization activity within privileged services.
- Implement endpoint monitoring for suspicious .NET behavior.
Official Patch / Upgrade
https://www.avira.com/en/support-download-avira-internet-security
CVE-2026-27748 – Symbolic Link Arbitrary File Deletion
Vulnerability Description
An arbitrary file deletion vulnerability was identified in the Avira Software Updater service. During update operations, the service deletes temporary or outdated files.
Improper validation of filesystem paths allows attackers to exploit symbolic links or NTFS reparse points.
If an attacker replaces a target file with a symbolic link pointing to another location, the privileged service may delete the linked file instead of the intended file.
Because the service runs with SYSTEM privileges, protected files belonging to the operating system may be removed.
Affected Component
Avira Software Updater Service
Exploitation Scenario
- A directory used by the updater service is identified.
- A file expected to be deleted during the update process is replaced with a symbolic link.
- The symbolic link points to a protected file.
- When the updater executes, the link is resolved and the protected file is deleted.
Security Impact
- Arbitrary file deletion
- System corruption
- Privilege escalation chaining
- Security product tampering
MITRE ATT&CK Mapping
| Technique | ID | Description |
|---|---|---|
| Hijack Execution Flow | T1574 | Abuse of symbolic links |
| Exploitation for Privilege Escalation | T1068 | Abuse of privileged service |
| Modify System Files | T1565 | Deletion of protected files |
Proof-of-Concept (Educational)
Example symbolic link creation:
mklink C:\ProgramData\Avira\tempfile.txt C:\Windows\System32\drivers\etc\hosts
If the updater service deletes tempfile.txt, the hosts file may be deleted instead.
Detection
Behavioral Indicators
- Creation of symbolic links in Avira update directories
- File deletion activity initiated by Avira updater service
- Unexpected deletion of protected operating system files
Log Sources
- Windows Security Event Logs
- Sysmon File Creation Logs
- Sysmon File Deletion Logs
- Endpoint Detection and Response telemetry
Detection Queries
Windows Event Log Query
EventID=4663
ProcessName="Avira*"
AccessMask="DELETE"
Sysmon Query
EventID=23
Image contains "Avira"
TargetFilename contains "Windows"
Splunk Query
index=windows EventCode=23
Image="*Avira*"
TargetFilename="*Windows*"
Elastic Query
process.name : "Avira*" AND event.action : "file_delete"
Mitigation
- Upgrade Avira Internet Security to the latest vendor release.
- Monitor creation of symbolic links within application directories.
- Restrict modification permissions for update directories.
- Enable filesystem monitoring policies.
Official Patch / Upgrade
https://www.avira.com/en/support-download-avira-internet-security
