CVE-2017-2193 in Tera Term
Summary
by MITRE
Untrusted search path vulnerability in the installer of Tera Term 4.94 and earlier allows an attacker to gain privileges via a Trojan horse DLL in an unspecified directory.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 12/27/2020
The vulnerability identified as CVE-2017-2193 represents a critical untrusted search path weakness in the Tera Term terminal emulator installer version 4.94 and earlier. This flaw exists within the installer component that handles the installation process of the Tera Term software, creating a security risk that can be exploited by malicious actors to elevate privileges on affected systems. The vulnerability stems from the installer's improper handling of dynamic link library loading mechanisms during the installation process, where it fails to validate or restrict the search path used to locate required libraries.
The technical implementation of this vulnerability involves the installer's reliance on a predictable search order for dynamic link libraries without proper validation of library sources. When the installer executes, it searches through a series of directories in a specific order to locate required DLL files, but this search mechanism does not adequately verify the authenticity or integrity of the libraries found. An attacker can exploit this by placing a malicious Trojan horse DLL in one of the directories that the installer searches before the legitimate system directories, causing the installer to load and execute the malicious code with elevated privileges. This behavior aligns with CWE-426, which describes untrusted search path vulnerabilities where applications execute code from untrusted locations due to improper path resolution.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to gain complete control over affected systems. The installer typically runs with elevated privileges due to the nature of software installation processes, making this vulnerability particularly dangerous. Once exploited, the malicious DLL can perform various malicious activities including but not limited to data exfiltration, system modification, or establishing persistent access. The vulnerability affects systems where Tera Term is installed or where the installer is executed, potentially compromising a wide range of environments including corporate networks, development workstations, and user endpoints.
Organizations and system administrators should immediately update to Tera Term version 4.95 or later, which contains the necessary patches to address this vulnerability. The mitigation strategy involves not only updating the software but also implementing proper access controls and monitoring for unauthorized DLL placement in system directories. Security controls should include regular vulnerability assessments, implementation of application whitelisting policies, and monitoring for suspicious installation activities. This vulnerability demonstrates the importance of secure coding practices in installer components and aligns with ATT&CK technique T1059.001 for command and scripting interpreter usage, as the malicious code execution occurs through legitimate installation processes. Additionally, the vulnerability highlights the need for proper privilege separation and the implementation of secure library loading mechanisms as recommended in secure software development lifecycle practices and compliance with industry standards such as those outlined in the NIST Cybersecurity Framework and ISO 27001 security controls.