CVE-2005-4532 in scponly
Summary
by MITRE
scponlyc in scponly 4.1 and earlier, when the operating system supports LD_PRELOAD mechanisms, allows local users to execute arbitrary code with root privileges by creating a chroot directory in their home directory, hard linking to a system setuid application, and using a modified LD_PRELOAD to modify expected function calls in the setuid application.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability identified as CVE-2005-4532 represents a critical privilege escalation flaw in the scponly utility version 4.1 and earlier. This issue specifically targets systems that support LD_PRELOAD mechanisms, creating a dangerous exploitation vector for local attackers seeking elevated privileges. The vulnerability stems from the insecure handling of chroot environments and setuid application execution within the scponly framework. The flaw allows malicious users to manipulate the execution flow of system utilities by leveraging the dynamic linking mechanism that LD_PRELOAD provides.
The technical implementation of this vulnerability involves several key components that work together to enable privilege escalation. Attackers exploit the scponly utility's chroot functionality by creating a carefully crafted chroot directory in their home directory. Within this directory, they establish hard links to system setuid applications, particularly those that are vulnerable to LD_PRELOAD manipulation. The exploitation relies on the fact that scponly, when running with root privileges, executes these setuid applications within the modified chroot environment. The attacker modifies the LD_PRELOAD environment variable to point to a malicious shared library that intercepts and modifies function calls expected by the setuid application, effectively bypassing normal security checks and gaining root access.
This vulnerability demonstrates a fundamental flaw in how setuid applications interact with dynamic linking mechanisms in chroot environments. The issue is particularly concerning because it operates at the system level where privilege separation should be maintained. The exploitation chain leverages the principle that setuid applications running in chrooted environments may still be subject to environment variable manipulation, particularly those that control dynamic linking behavior. The vulnerability represents a classic case of insufficient input validation and environment sanitization, allowing attackers to manipulate the execution context of privileged processes through carefully crafted file system links and environment modifications.
The operational impact of CVE-2005-4532 is severe and far-reaching for systems that rely on scponly for secure file transfer operations. Local users who can access the system with low privileges can escalate their access to full root privileges, potentially compromising the entire system. This vulnerability affects systems where scponly is used as a restricted shell or file transfer mechanism, particularly in multi-user environments where users require limited access to file transfer capabilities but should not be able to escalate privileges. The attack vector is particularly insidious because it requires minimal privileges to initiate and can be executed without requiring network access or complex exploitation techniques.
From a cybersecurity perspective, this vulnerability aligns with several ATT&CK framework techniques including privilege escalation through dynamic-link library (DLL) injection and exploitation of environment variables. The vulnerability also relates to CWE-428, which addresses "Unquoted Search Path or Library Load," and CWE-276, concerning "Incorrect Default Permissions." Organizations should implement immediate mitigations including updating to scponly versions that address this vulnerability, implementing proper environment variable sanitization, and ensuring that setuid applications are not susceptible to LD_PRELOAD manipulation. System administrators should also consider implementing monitoring for unusual hard link creation patterns and chroot directory modifications. The vulnerability underscores the importance of proper privilege separation and environment isolation, particularly in restricted shell implementations and chroot environments where attackers may attempt to exploit dynamic linking mechanisms to bypass security controls.