CVE-2017-12840 in DESLock+
Summary
by MITRE
A kernel driver, namely DLMFENC.sys, bundled with the DESLock+ client application 4.8.16 and earlier contains a locally exploitable heap based buffer overflow in the handling of an IOCTL message of type 0x0FA4204. The vulnerability is present due to the kernel driver failing to allocate sufficient memory on the kernel heap to contain a user supplied string as such the string is copied into a buffer of constant size (0x1000-bytes) and thus an overflow condition results. Access to the kernel driver is permitted through an obfuscated interface whereby bytes of user supplied message are "authenticated" via an obfuscation routine employing a linear equation.
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Analysis
by VulDB Data Team • 11/10/2019
The vulnerability described in CVE-2017-12840 represents a critical heap-based buffer overflow within the DLMFENC.sys kernel driver component of DESLock+ client software version 4.8.16 and earlier. This flaw exists within the kernel space of the operating system, making it particularly dangerous as it can be exploited to execute arbitrary code with kernel-level privileges. The vulnerability manifests specifically during the processing of IOCTL (Input/Output Control) messages with the identifier 0x0FA4204, which is a well-defined mechanism for communicating with kernel drivers from user-space applications. The kernel driver's failure to properly validate and allocate memory for user-supplied data creates a condition where a maliciously crafted input string can exceed the predetermined buffer boundaries, leading to memory corruption that can be leveraged for privilege escalation attacks.
The technical implementation of this vulnerability stems from the driver's inadequate memory management practices during the processing of user input. Specifically, the kernel driver allocates a fixed-size buffer of exactly 0x1000 bytes (4096 bytes) regardless of the actual size of the user-provided string data. When a user supplies a string longer than this predetermined limit, the copy operation overflows the buffer and writes beyond its allocated memory boundaries, potentially corrupting adjacent memory structures. This heap-based overflow condition creates opportunities for attackers to manipulate kernel memory layout, potentially leading to arbitrary code execution or system crashes. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though in this case it manifests as a heap-based condition due to the kernel driver's memory allocation patterns and the nature of the affected buffer.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete system compromise, as the attacker gains kernel-level access to the target system. This level of access allows for persistent backdoor installation, full system enumeration, data exfiltration, and complete bypass of operating system security mechanisms. The obfuscated interface mechanism employed by the driver adds complexity to exploitation attempts, as the attacker must first reverse-engineer the obfuscation routine that uses a linear equation to authenticate bytes of the user-supplied message. This obfuscation technique, while intended to provide some security through obscurity, ultimately fails to prevent exploitation as the underlying buffer overflow remains intact. The vulnerability is particularly concerning because it affects a widely deployed security solution, meaning that successful exploitation could provide attackers with access to protected systems that are specifically designed to prevent unauthorized access.
Mitigation strategies for this vulnerability require immediate action from system administrators and security teams. The primary and most effective mitigation is the immediate upgrade of DESLock+ client software to version 4.8.17 or later, which contains the patched kernel driver that properly validates input lengths before memory allocation. System administrators should also implement monitoring of kernel driver access patterns and unusual IOCTL activity that might indicate exploitation attempts. The vulnerability's classification under the ATT&CK framework places it within the privilege escalation category, specifically under techniques that leverage kernel vulnerabilities for system compromise. Additional defensive measures include restricting access to the vulnerable kernel driver through registry modifications or group policy controls, implementing driver signature enforcement, and conducting thorough system audits to detect any potential exploitation attempts. Organizations should also consider deploying endpoint detection and response solutions that can identify anomalous behavior indicative of kernel-level attacks, as traditional antivirus solutions may not detect such sophisticated exploits targeting kernel drivers directly.