CVE-2020-3979 in InstallBuilder for Qt Windows
Summary
by MITRE
InstallBuilder for Qt Windows (versions prior to 20.7.0) installers look for plugins at a predictable location at initialization time, writable by non-admin users. While those plugins are not required, they are loaded if present, which could allow an attacker to plant a malicious library which could result in code execution with the security scope of the installer.
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Analysis
by VulDB Data Team • 09/19/2020
The vulnerability identified as CVE-2020-3979 affects InstallBuilder for Qt Windows installations prior to version 20.7.0, presenting a significant security risk through improper plugin loading mechanisms. This flaw resides in the installer's initialization process where it systematically searches for plugins at a predetermined location that lacks proper access controls. The vulnerability stems from the installer's design philosophy that allows plugin loading from user-writable directories, creating an attack surface that adversaries can exploit to gain unauthorized code execution privileges. The issue is particularly concerning because it operates under the assumption that plugins are optional components while simultaneously providing a mechanism for their automatic loading when present, without adequate validation or security checks.
The technical implementation of this vulnerability demonstrates a classic path traversal and privilege escalation flaw where the installer's plugin discovery mechanism fails to properly validate the security context of plugin locations. The predictable directory structure combined with write permissions for non-administrative users creates a scenario where malicious actors can place specially crafted libraries in the designated plugin path. This design flaw directly relates to CWE-276 which addresses incorrect permissions for critical resources, and CWE-427 which covers uncontrolled search path elements. The installer's behavior of automatically loading plugins from user-accessible locations without proper sandboxing or privilege validation creates an inherent risk that can be exploited through simple file placement attacks. Attackers can leverage this weakness to execute arbitrary code with the same security context as the installer process, potentially escalating privileges or compromising the entire installation environment.
The operational impact of CVE-2020-3979 extends beyond simple code execution as it represents a fundamental flaw in the installer's security architecture that can be exploited during legitimate installation processes. When users run installers that are vulnerable to this issue, they unknowingly create an environment where malicious code can be injected and executed with elevated privileges. The attack vector is particularly dangerous because it requires no special privileges beyond basic user access, making it accessible to a broad range of potential attackers. This vulnerability can be exploited in various scenarios including targeted attacks against specific organizations, supply chain compromises where legitimate installers are modified, or general malware distribution through compromised installer packages. The risk is amplified by the fact that many users may not be aware of the security implications of running installers from untrusted sources, especially when these installers are part of legitimate software distributions.
Mitigation strategies for CVE-2020-3979 primarily focus on upgrading to InstallBuilder version 20.7.0 or later, which addresses the plugin loading vulnerability through improved access controls and validation mechanisms. Organizations should implement comprehensive patch management processes to ensure all vulnerable installers are updated promptly, particularly in environments where software installation occurs with elevated privileges. System administrators should consider implementing additional security measures such as restricting write permissions to plugin directories, monitoring for unauthorized file modifications in installation paths, and deploying application whitelisting policies to prevent execution of untrusted binaries. The vulnerability also highlights the importance of following security best practices such as the principle of least privilege and secure coding guidelines that prevent predictable paths from being writable by unprivileged users. Organizations should also consider implementing behavioral monitoring and intrusion detection systems that can identify suspicious plugin loading activities or attempts to modify installation directories, as recommended by the MITRE ATT&CK framework's techniques for privilege escalation and persistence mechanisms.