CVE-2018-9336 in OpenVPN
Summary
by MITRE
openvpnserv.exe (aka the interactive service helper) in OpenVPN 2.4.x before 2.4.6 allows a local attacker to cause a double-free of memory by sending a malformed request to the interactive service. This could cause a denial-of-service through memory corruption or possibly have unspecified other impact including privilege escalation.
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Analysis
by VulDB Data Team • 03/08/2023
The vulnerability identified as CVE-2018-9336 affects the openvpnserv.exe component within OpenVPN versions 2.4.x prior to 2.4.6, specifically targeting the interactive service helper functionality. This flaw represents a critical memory corruption issue that arises from improper handling of malformed requests sent to the interactive service. The vulnerability exists within the Windows service implementation that facilitates user interaction with OpenVPN's core functionality, creating a pathway for local attackers to exploit memory management errors through crafted input sequences.
The technical root cause of this vulnerability stems from a double-free memory error condition that occurs when the interactive service helper processes malformed requests. This type of vulnerability is classified as a memory safety issue and corresponds to CWE-415, which addresses double-free conditions in memory management. When the service receives an improperly formatted request, it attempts to free the same memory block twice, leading to corruption of the heap management structures. The flaw manifests in the service's request processing loop where insufficient validation occurs before memory deallocation operations, allowing an attacker to manipulate the service into executing invalid memory operations.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions to potentially enable privilege escalation attacks. While the primary consequence is memory corruption that can cause system instability and service termination, the underlying heap corruption presents opportunities for more sophisticated exploitation techniques. Attackers could potentially leverage this vulnerability to execute arbitrary code with elevated privileges, particularly since the interactive service helper typically operates with higher permissions than standard user processes. The vulnerability's local attack vector means that an attacker must already have access to the system, but the potential for privilege escalation makes it particularly concerning for environments where multiple users share systems or where service accounts have elevated privileges.
Mitigation strategies for CVE-2018-9336 primarily focus on immediate patch deployment to OpenVPN 2.4.6 or later versions where the memory management issues have been resolved. System administrators should prioritize updating all affected OpenVPN installations and verify that the interactive service helper component has been properly patched. Additionally, implementing proper access controls and limiting local user access to systems running vulnerable OpenVPN versions can reduce exploitation risk. Network segmentation and monitoring for unusual service behavior or memory allocation patterns can help detect potential exploitation attempts. Organizations should also consider implementing application whitelisting policies that restrict execution of unauthorized binaries, particularly those that might attempt to interact with the vulnerable service components. The vulnerability's classification under ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', underscores the need for comprehensive endpoint protection measures and regular security assessments to prevent exploitation of such memory corruption vulnerabilities.