CVE-2020-25744 in SaferVPN
Summary
by MITRE
SaferVPN before 5.0.3.3 on Windows could allow low-privileged users to create or overwrite arbitrary files, which could cause a denial of service (DoS) condition, because a symlink from %LOCALAPPDATA%\SaferVPN\Log is followed.
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Analysis
by VulDB Data Team • 09/18/2020
This vulnerability exists in SaferVPN versions prior to 5.0.3.3 on Windows operating systems and represents a classic symlink traversal flaw that can be exploited by low-privileged users to manipulate the application's file system behavior. The vulnerability stems from the application's improper handling of symbolic links within the %LOCALAPPDATA%\SaferVPN\Log directory path, which allows unauthorized users to create or overwrite arbitrary files in the system. The flaw specifically manifests when the application follows symbolic links without proper validation, enabling attackers to redirect file operations to sensitive system locations. This issue falls under CWE-382 which specifically addresses the use of symbolic links inappropriately, and represents a privilege escalation vector that can be leveraged to cause system instability. The vulnerability is particularly concerning because it operates at the file system level and can be exploited by users with minimal privileges, making it an attractive target for attackers seeking to disrupt service availability or potentially escalate their access rights.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can be weaponized to overwrite critical system files or create malicious files that persist across system reboots. When low-privileged users can manipulate the symbolic link resolution process, they effectively gain the ability to modify files in locations where they would normally not have write permissions. This creates a potential attack surface that could be exploited to inject malicious code or corrupt application data, leading to more severe consequences than simple DoS conditions. The vulnerability aligns with ATT&CK technique T1059.001 which covers command and scripting interpreter usage, and T1566 which addresses credential harvesting through social engineering, as attackers could leverage this flaw to establish persistence. The specific path manipulation occurs in the local application data directory, which is typically used for storing application-specific data and logs, making it a logical target for attackers seeking to maintain control over the system.
Mitigation strategies for this vulnerability should focus on implementing proper symbolic link validation and ensuring that applications do not follow symbolic links in sensitive directories without explicit user consent or administrative privileges. The most effective remediation involves updating to SaferVPN version 5.0.3.3 or later, which includes proper validation of symbolic link resolution. System administrators should also implement strict access controls on the %LOCALAPPDATA%\SaferVPN\Log directory and consider using Windows file permissions to restrict symbolic link creation capabilities. Additionally, the principle of least privilege should be enforced by ensuring that application processes run with minimal required permissions and that symbolic link creation is restricted to authorized users only. Organizations should also monitor for suspicious file creation patterns in application data directories and implement security awareness training to prevent exploitation through social engineering attacks that might attempt to leverage this vulnerability. The fix should include proper input validation and sanitization of file paths, ensuring that any symbolic link resolution is performed in a secure context that prevents unauthorized file system manipulation.