CVE-2018-6851 in SafeGuard Enterprise
Summary
by MITRE
Sophos SafeGuard Enterprise before 8.00.5, SafeGuard Easy before 7.00.3, and SafeGuard LAN Crypt before 3.95.2 are vulnerable to Local Privilege Escalation via IOCTL 0x80206040. By crafting an input buffer we can control the execution path to the point where the constant DWORD 0 will be written to a user-controlled address. We can take advantage of this condition to zero-out the pointer to the security descriptor in the object header of a privileged process or modify the security descriptor itself and run code in the context of a process running as SYSTEM.
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Analysis
by VulDB Data Team • 03/03/2020
The vulnerability described in CVE-2018-6851 represents a critical local privilege escalation flaw affecting multiple Sophos SafeGuard products including SafeGuard Enterprise versions prior to 8.00.5, SafeGuard Easy versions prior to 7.00.3, and SafeGuard LAN Crypt versions prior to 3.95.2. This issue stems from improper input validation within the kernel-mode drivers of these security products, specifically when handling IOCTL (Input/Output Control) requests with the identifier 0x80206040. The flaw allows attackers with local access to manipulate memory structures in ways that can fundamentally alter the security context of running processes.
The technical exploitation of this vulnerability occurs through a carefully crafted input buffer that manipulates the execution flow of the affected driver. The flaw manifests when a constant DWORD value of 0 is written to a memory address controlled by the attacker, which can be positioned to target the object header of privileged processes. This particular memory location typically contains critical security descriptors that govern access permissions to kernel objects. When the attacker successfully overwrites this pointer or modifies the security descriptor itself, they gain the ability to manipulate process permissions and execute code within the context of a process running with SYSTEM privileges.
The operational impact of this vulnerability is severe as it provides a direct pathway for local attackers to escalate their privileges from standard user level to SYSTEM level without requiring additional exploitation techniques. This privilege escalation occurs entirely within the kernel space of the operating system, making it particularly dangerous since it bypasses normal user-mode security controls and access checks. The vulnerability essentially allows an attacker to modify the security metadata of kernel objects, effectively granting them unauthorized access to system resources and potentially enabling complete system compromise. The attack vector is relatively straightforward as it requires only local access to the system and the ability to submit malicious IOCTL requests to the vulnerable drivers.
This vulnerability maps directly to CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation'. The flaw demonstrates a classic case of improper input validation leading to memory corruption, where the attacker can control both the data being written and the target memory location. The exploitation process leverages the kernel-mode nature of the vulnerability to modify critical security structures, making it particularly effective for privilege escalation attacks. Organizations should immediately apply the vendor-provided patches to all affected versions, as this vulnerability can be exploited by any local user to gain SYSTEM-level access to the compromised systems.
The attack scenario typically begins with a local user executing a malicious program that sends crafted IOCTL requests to the vulnerable SafeGuard drivers. The kernel driver processes this input without proper validation, allowing the attacker to write a zero value to a controlled memory address. When this address points to a security descriptor within a privileged process object header, the modification effectively strips away access controls, enabling the attacker to execute code with elevated privileges. This type of vulnerability is particularly concerning because it can be exploited by malware or malicious users who have gained initial access to a system through other means, providing a reliable path to full system compromise.