CVE-2014-0979 in openSUSE
Summary
by MITRE
The start_authentication function in lightdm-gtk-greeter.c in LightDM GTK+ Greeter before 1.7.1 does not properly handle the return value from the lightdm_greeter_get_authentication_user function, which allows local users to cause a denial of service (NULL pointer dereference) via an empty username.
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Analysis
by VulDB Data Team • 12/20/2024
The vulnerability identified as CVE-2014-0979 resides within the LightDM GTK+ Greeter component of the Linux display manager ecosystem, specifically affecting versions prior to 1.7.1. This issue manifests in the start_authentication function where improper handling of return values from lightdm_greeter_get_authentication_user creates a critical security flaw. The flaw represents a classic null pointer dereference condition that can be exploited by local attackers to disrupt system operations. LightDM serves as a crucial graphical login interface for numerous Linux distributions, making this vulnerability particularly concerning as it directly impacts the authentication process that users rely upon for system access.
The technical implementation of this vulnerability stems from a failure in input validation and error handling within the authentication flow. When the start_authentication function processes user credentials, it calls lightdm_greeter_get_authentication_user to retrieve the authentication user information. However, the function does not adequately check whether this call returns a valid user object or a NULL value. In scenarios where an empty username is provided, the system fails to properly validate the return value before proceeding with authentication operations. This oversight creates a condition where the application attempts to dereference a NULL pointer, leading to an immediate crash of the greeter process and subsequent denial of service.
The operational impact of CVE-2014-0979 extends beyond simple service disruption as it affects the fundamental authentication mechanism that users depend on for system access. Local attackers can exploit this vulnerability by providing an empty username during the login process, causing the LightDM GTK+ Greeter to crash and forcing users to restart the authentication process or potentially lose access to their system. This type of denial of service vulnerability undermines user confidence in system stability and can be particularly problematic in enterprise environments where consistent access to login interfaces is critical. The vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions, and represents a failure in proper null pointer validation that violates security best practices.
Mitigation strategies for this vulnerability require immediate patching of affected LightDM GTK+ Greeter installations to version 1.7.1 or later, which contains the necessary code modifications to properly handle return values from authentication functions. System administrators should also implement monitoring solutions to detect unauthorized access attempts that might exploit this vulnerability, as well as establish robust logging mechanisms to track authentication failures. The fix implemented in the patched versions involves proper validation of return values from lightdm_greeter_get_authentication_user before proceeding with authentication operations, ensuring that NULL values are appropriately handled and that the system maintains stability even when invalid inputs are provided. Organizations should also consider implementing additional security controls such as access control lists and authentication policy enforcement to further reduce the attack surface and prevent exploitation of similar vulnerabilities in the authentication subsystem. This vulnerability demonstrates the importance of thorough input validation and proper error handling in security-critical components of system infrastructure, aligning with ATT&CK technique T1499 for denial of service attacks and emphasizing the need for secure coding practices in authentication systems.