CVE-2017-7720 in PrivateTunnel
Summary
by MITRE
Buffer overflow in PrivateTunnel 2.7 and 2.8 allows local attackers to cause a denial of service (SEH overwrite) or possibly have unspecified other impact via a long password.
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Analysis
by VulDB Data Team • 09/21/2020
The vulnerability identified as CVE-2017-7720 represents a critical buffer overflow flaw within the PrivateTunnel VPN client software version 2.7 and 2.8. This issue resides in the authentication handling mechanism where the application fails to properly validate the length of password input provided by users. The flaw manifests as a structured exception handler overwrite condition that occurs when an attacker provides an excessively long password string to the application. The vulnerability is classified as a local privilege escalation vector since it requires local system access to exploit, though it can potentially be leveraged for more severe consequences.
The technical implementation of this vulnerability stems from improper input validation within the password processing module of PrivateTunnel. When a user enters a password that exceeds the allocated buffer size, the application does not perform adequate bounds checking before copying the input data into memory. This results in memory corruption that overwrites the structured exception handler chain, which is a critical component of windows exception handling mechanisms. The CWE-121 classification applies here as this represents a classic stack-based buffer overflow vulnerability where insufficient bounds checking leads to memory corruption.
From an operational perspective, this vulnerability creates significant risk for systems running affected PrivateTunnel versions. While the primary impact is denial of service through structured exception handler corruption, the unspecified additional impacts could potentially include arbitrary code execution or privilege escalation depending on the execution context. The vulnerability affects any local user who can interact with the PrivateTunnel client, making it particularly concerning in multi-user environments where local access might be obtained through various attack vectors. This aligns with ATT&CK technique T1068 which covers local privilege escalation through exploitation of software vulnerabilities.
The exploitation of this vulnerability requires minimal prerequisites since it only needs local access to the system and the ability to interact with the PrivateTunnel client application. Attackers can leverage this flaw to disrupt service availability or potentially escalate privileges if the application runs with elevated permissions. The impact extends beyond simple denial of service as the structured exception handler overwrite can cause unpredictable application behavior and system instability. Organizations should consider this vulnerability in their risk assessment frameworks, particularly when evaluating the security posture of systems running legacy VPN client software. Mitigation strategies should include immediate patch deployment, implementation of input validation controls, and monitoring for suspicious authentication attempts that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and memory management practices in client-side applications, particularly those handling authentication credentials where buffer overflows can lead to severe security implications.