CVE-2018-6318 in Tester Tool
Summary
by MITRE
In Sophos Tester Tool 3.2.0.7 Beta, the driver loads (in the context of the application used to test an exploit or ransomware) the DLL using a payload that runs from NTDLL.DLL (so, it's run in userland), but the driver doesn't perform any validation of this DLL (not its signature, not its hash, etc.). A person can change this DLL in a local way, or with a remote connection, to a malicious DLL with the same name -- and when the product is used, this malicious DLL will be loaded, aka a DLL Hijacking attack.
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Analysis
by VulDB Data Team • 01/01/2020
The vulnerability identified in Sophos Tester Tool version 3.2.0.7 Beta represents a critical DLL hijacking flaw that exploits improper dynamic link library loading mechanisms within the application's driver component. This vulnerability falls under the Common Weakness Enumeration category CWE-427 and aligns with the MITRE ATT&CK technique T1059.001 for execution through system processes. The Sophos Tester Tool is designed to evaluate exploit and ransomware scenarios, making it a privileged application that operates with elevated privileges during testing activities. The core technical flaw occurs when the driver loads a DLL from NTDLL.DLL context, which operates in userland, but fails to implement any form of validation checks including digital signature verification or cryptographic hash comparison. This lack of validation creates an exploitable condition where an attacker can substitute the legitimate DLL with a malicious counterpart that maintains the same filename, effectively bypassing the application's security controls. The vulnerability is particularly concerning because it operates in a testing environment that is expected to be secure and isolated, yet provides a pathway for privilege escalation through the manipulation of dynamic loading processes.
The operational impact of this vulnerability extends beyond simple code execution as it enables a sophisticated attack vector that can be leveraged for privilege escalation and persistent access within the target system. When an attacker successfully replaces the legitimate DLL with a malicious one, the application will load and execute the attacker-controlled code with the privileges of the application itself, which typically includes system-level access due to the nature of the testing tool. The attack can be executed locally or remotely, providing attackers with multiple vectors for exploitation. The persistence mechanism is particularly dangerous because the malicious DLL will be loaded every time the Sophos Tester Tool is executed, creating a stealthy backdoor that can remain active across system reboots. This vulnerability demonstrates a fundamental flaw in the application's trust model where the system assumes that DLLs loaded through the driver component are legitimate without proper verification mechanisms, creating a trust boundary that can be easily compromised.
Mitigation strategies for this vulnerability must address both the immediate security gap and the underlying architectural issues that allowed the flaw to exist. The most effective immediate solution involves implementing strict DLL validation mechanisms including digital signature verification and cryptographic hash checks before any DLL is loaded into the application's memory space. Organizations should also implement application whitelisting policies that prevent unauthorized DLL execution, particularly in privileged applications. The recommended approach includes configuring the application to use absolute paths for DLL loading rather than relative paths, and implementing secure DLL search order mechanisms that prioritize system directories over user-controllable locations. Additionally, regular security audits should be conducted to identify similar vulnerabilities in other applications and drivers within the system. The vulnerability highlights the importance of the principle of least privilege and proper input validation, as outlined in the OWASP Top Ten and NIST cybersecurity frameworks, where applications should never trust external inputs without proper verification mechanisms. System administrators should also monitor for unauthorized DLL modifications through file integrity monitoring solutions and implement network-based controls to prevent remote exploitation attempts. The remediation process should include comprehensive testing to ensure that legitimate DLL functionality remains intact while malicious DLLs are properly blocked.