CVE-2015-9267 in Scriptable Install System
Summary
by MITRE
Nullsoft Scriptable Install System (NSIS) before 2.49 uses temporary folder locations that allow unprivileged local users to overwrite files. This allows a local attack in which either a plugin or the uninstaller can be replaced by a Trojan horse program.
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Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2015-9267 affects Nullsoft Scriptable Install System version 2.49 and earlier, representing a significant local privilege escalation risk within Windows installation environments. This flaw resides in the temporary folder handling mechanisms employed by NSIS during installation and uninstallation processes, creating persistent security weaknesses that can be exploited by unprivileged users to gain elevated system access. The vulnerability stems from the improper management of temporary file locations, which are created with insufficient security controls and predictable naming conventions. Attackers can leverage this weakness to replace legitimate installation components with malicious Trojan horse programs, effectively compromising the integrity of the installation process.
The technical implementation of this vulnerability involves NSIS creating temporary files in standard system directories without adequate permission controls or randomization of file names. When installation or uninstallation processes execute, they utilize these predictable temporary locations where unprivileged users can place malicious files that will be executed with elevated privileges. This design flaw allows attackers to substitute legitimate plugins or uninstaller components with malicious equivalents, creating a persistent backdoor within the target system. The vulnerability operates at the file system level and relies on the principle of least privilege being violated during installation procedures, where temporary files are created with overly permissive access controls.
From an operational impact perspective, this vulnerability enables local attackers to achieve privilege escalation without requiring administrative credentials or complex exploitation techniques. The attack vector is particularly concerning because it targets the installation infrastructure itself, meaning that any system running vulnerable NSIS installations could be compromised through simple file replacement attacks. The attack requires minimal skill level and can be executed through basic file system manipulation, making it accessible to a wide range of threat actors. The compromise of installation processes creates long-term persistence mechanisms, as the replaced components continue to execute with elevated privileges during subsequent system operations.
Security professionals should address this vulnerability through immediate patching of NSIS installations to version 2.49 or later, which implements proper temporary file handling with secure permissions and randomized naming conventions. Additional mitigations include implementing strict file system permissions on temporary directories, monitoring for unauthorized file modifications in installation-related directories, and employing application whitelisting controls to prevent execution of unauthorized installation components. The vulnerability aligns with CWE-377, which addresses insecure temporary file handling, and represents a clear violation of the principle of least privilege in software design. Organizations should also consider implementing endpoint detection and response solutions to monitor for suspicious installation activities and file system modifications that could indicate exploitation attempts. This vulnerability demonstrates the critical importance of secure temporary file management in installation systems and highlights the need for comprehensive security testing of installation frameworks to prevent similar issues in other software components.