CVE-2017-2220 in CASL II Simulator
Summary
by MITRE
Untrusted search path vulnerability in Installer of CASL II simulator (self-extract format) allows an attacker to gain privileges via a Trojan horse DLL in an unspecified directory.
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Analysis
by VulDB Data Team • 10/24/2019
The vulnerability identified as CVE-2017-2220 represents a critical untrusted search path issue within the Installer component of the CASL II simulator application. This software vulnerability specifically affects the self-extract format installation mechanism, creating a dangerous condition where malicious actors can manipulate the software installation process to execute arbitrary code with elevated privileges. The CASL II simulator is a widely used educational tool for teaching computer architecture and assembly language programming, making this vulnerability particularly concerning for academic and research environments where such systems are prevalent.
The technical flaw stems from improper handling of dynamic library loading during the installation process. When the CASL II installer executes, it searches for required DLL files in a predictable sequence of directories without adequate validation of the source or integrity of these components. This behavior creates a race condition where an attacker can place a malicious Trojan horse DLL in a directory that gets searched before the legitimate system directories. The installer's trust model assumes that all DLLs in its search path are legitimate, which violates fundamental security principles of least privilege and input validation. This vulnerability maps directly to CWE-426, which describes the dangerous practice of allowing untrusted search paths to be used for loading dynamic libraries, and can be categorized under ATT&CK technique T1059.001 for execution through command and scripting interpreter.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable complete system compromise through a relatively simple attack vector. An attacker with access to write permissions in the targeted directory can replace legitimate DLLs with malicious counterparts, potentially gaining administrative privileges or executing arbitrary code with the privileges of the user running the installer. The self-extract format of the CASL II simulator makes this attack particularly dangerous because the installer often runs with elevated privileges, and the extraction process typically occurs in user-accessible temporary directories. This vulnerability affects not only individual users but also entire organizations that deploy this simulator in educational or research settings, where multiple users may have varying levels of access to the installation directories.
Mitigation strategies for CVE-2017-2220 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves applying the vendor-provided patch or upgrade to the CASL II simulator software, which should address the untrusted search path implementation by either using absolute paths for library loading or implementing proper DLL verification mechanisms. Organizations should also implement directory permission controls to prevent unauthorized modifications to installation directories, particularly those containing the CASL II simulator installation files. System administrators should consider implementing application whitelisting policies that restrict which DLLs can be loaded by the installer process, and regular security audits should verify that no malicious DLLs exist in the installation search paths. Additionally, users should be educated about the risks of running installers from untrusted sources and the importance of maintaining secure installation environments. The vulnerability serves as a prime example of why modern software development practices must incorporate secure coding principles and why organizations should maintain up-to-date security patches across all software installations.