CVE-2011-5054 in kcheckpass
Summary
by MITRE
kcheckpass passes a user-supplied argument to the pam_start function, often within a setuid environment, which allows local users to invoke any configured PAM stack, and possibly trigger unintended side effects, via an arbitrary valid PAM service name, a different vulnerability than CVE-2011-4122. NOTE: the vendor indicates that the possibility of resultant privilege escalation may be "a bit far-fetched."
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Analysis
by VulDB Data Team • 04/12/2019
The vulnerability described in CVE-2011-5054 resides within the kcheckpass utility, a component commonly found in KDE-based Linux distributions that handles authentication for various desktop services. This utility operates in a setuid context, meaning it runs with elevated privileges to perform authentication tasks that require system-level access. The flaw occurs when kcheckpass accepts user-supplied arguments and directly passes them to the pam_start function without adequate validation or sanitization. This design oversight creates a critical security risk as it allows local attackers to manipulate the PAM service name parameter, effectively bypassing normal authentication controls and potentially accessing unauthorized PAM modules or configurations.
The technical nature of this vulnerability aligns with CWE-20, "Improper Input Validation," and represents a classic case of insecure parameter handling within privileged code execution contexts. When kcheckpass receives a user-provided argument, it directly feeds this input into the PAM authentication framework through pam_start, which typically expects a predefined service name from a system configuration file. However, due to the lack of input validation, an attacker can specify any valid PAM service name, potentially triggering alternative authentication paths or modules that were not intended to be accessible through the normal user interface. This behavior creates a potential attack surface that could enable exploitation of other underlying vulnerabilities within the PAM stack or allow access to unintended system resources.
From an operational perspective, this vulnerability presents significant risks to system security, particularly in multi-user environments where local privilege escalation remains a primary concern. While the vendor's assessment suggests that privilege escalation may be "a bit far-fetched," the potential for unintended side effects cannot be dismissed entirely, especially when considering that PAM modules can have varying levels of access and functionality. Attackers could potentially leverage this vulnerability to trigger specific PAM modules that might have their own security flaws or to access authentication mechanisms that should remain restricted. The impact extends beyond simple authentication bypass, as the PAM framework itself can be configured to perform various actions including logging, account management, or even execute arbitrary commands depending on the module configuration.
The security implications of CVE-2011-5054 align with several ATT&CK techniques including T1068, "Exploitation for Privilege Escalation," and T1548.003, "Abuse Elevation Control Mechanism: Sudo and Sudo Caching." The vulnerability demonstrates how insufficient input validation in setuid programs can create pathways for attackers to manipulate system authentication flows and potentially gain unauthorized access to system resources. Organizations should consider implementing additional controls such as restricting access to kcheckpass, monitoring for unusual PAM service name usage, and ensuring that PAM configuration files are properly secured to prevent unauthorized module access. Regular security audits of setuid programs and their input handling mechanisms remain essential for identifying similar vulnerabilities that could provide attackers with elevated privileges or access to sensitive system functions.