CVE-2019-11230 in Avast
Summary
by MITRE
In Avast Antivirus before 19.4, a local administrator can trick the product into renaming arbitrary files by replacing the Logs\Update.log file with a symlink. The next time the product attempts to write to the log file, the target of the symlink is renamed. This defect can be exploited to rename a critical product file (e.g., AvastSvc.exe), causing the product to fail to start on the next system restart.
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Analysis
by VulDB Data Team • 11/01/2023
The vulnerability identified as CVE-2019-11230 represents a significant local privilege escalation flaw within Avast Antivirus software versions prior to 19.4. This issue stems from improper handling of file operations during the logging process, specifically when the application attempts to write to the Update.log file located in the Logs directory. The flaw allows a local administrator with sufficient privileges to manipulate the system's file structure in a way that compromises the integrity of the antivirus product itself. The vulnerability manifests when an attacker creates a symbolic link that points to a critical system file, such as AvastSvc.exe, and then replaces the legitimate log file with this symlink. This design flaw creates a race condition scenario where the antivirus service, while attempting to maintain its operational logs, inadvertently executes the symlink target instead of writing to the intended log file location. The technical implementation of this vulnerability aligns with CWE-617, which addresses reachable assertion conditions, and more specifically relates to CWE-22, representing improper limitation of a pathname to a restricted directory, commonly known as path traversal attacks.
The operational impact of this vulnerability extends beyond simple file manipulation, creating a potential pathway for complete system compromise. When the Avast service attempts to write to what it believes is the Update.log file, it actually performs the rename operation on the symlink target, which could be any file within the system's file structure. This means that an attacker could redirect the service to rename critical system files, including the core antivirus service executable itself, thereby preventing the product from functioning properly upon system restart. The attack vector is particularly dangerous because it requires only local administrator privileges, which are often more accessible than remote attack surfaces, and the exploitation process is relatively straightforward. The vulnerability demonstrates a classic case of insufficient input validation and improper file handling practices, where the software assumes that all files in its operational directories are legitimate without proper verification of file types or symbolic link status. This type of flaw is particularly concerning in security software, as it creates an inherent weakness that allows attackers to undermine the very protection mechanisms designed to defend against threats.
The exploitation of CVE-2019-11230 aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence mechanisms. Attackers could leverage this vulnerability to establish a foothold that allows them to maintain access while simultaneously disabling security protections. The technique of replacing legitimate log files with symbolic links to critical system components represents a form of file system manipulation that can be categorized under the ATT&CK tactic of Privilege Escalation through Process Injection or File System Permissions. Organizations should be aware that this vulnerability can be exploited as part of a broader attack chain where initial access might be gained through other means, but this particular flaw provides a reliable method for maintaining control while subverting security defenses. The remediation approach involves updating to Avast Antivirus version 19.4 or later, which includes proper validation of file types and prevents the creation of symbolic links in critical operational directories. Additionally, system administrators should implement strict file system permissions and monitoring to detect unauthorized symbolic link creation in sensitive directories. The vulnerability also highlights the importance of proper input validation and the principle of least privilege in security software design, where applications should never trust file system operations without verifying the integrity and type of target files before executing operations against them.