CVE-2013-4459 in LightDM
Summary
by MITRE
LightDM 1.7.5 through 1.8.3 and 1.9.x before 1.9.2 does not apply the AppArmor profile to the Guest account, which allows local users to bypass intended restrictions by leveraging the Guest account.
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Analysis
by VulDB Data Team • 12/25/2024
LightDM serves as a graphical display manager for unix-like operating systems and is widely deployed across various linux distributions including ubuntu and debian. The vulnerability in question affects versions 1.7.5 through 1.8.3 and 1.9.x before 1.9.2 where the application fails to properly enforce AppArmor security policies for guest user sessions. This flaw represents a significant bypass of the intended security controls that should restrict guest accounts from accessing system resources and executing privileged operations. The vulnerability is classified under CWE-284 Access Control Bypass, which specifically addresses situations where improper access control mechanisms allow unauthorized access to protected resources.
The technical implementation flaw stems from how LightDM handles the application of security profiles during guest session initialization. When a guest account is created or accessed, the system should automatically apply the appropriate AppArmor profile to restrict the guest session's capabilities and prevent privilege escalation. However, in the affected versions, this profile application mechanism fails for guest accounts specifically, leaving them without the intended security boundaries. This creates a scenario where local users can leverage the guest account functionality to execute commands that would normally be restricted, effectively bypassing the security controls that should isolate guest sessions from the underlying system.
The operational impact of this vulnerability is substantial as it provides local attackers with a means to circumvent security restrictions that are fundamental to system integrity. An attacker with access to a guest account can potentially escalate privileges, access restricted files, or execute unauthorized operations that should be prevented by the AppArmor profile. This vulnerability particularly affects systems where guest access is enabled and where the security model relies on proper session isolation. The impact extends beyond simple privilege escalation as it undermines the entire security architecture that depends on proper session management and access control enforcement. The flaw enables a persistent threat vector that can be exploited by any local user who gains access to the guest account functionality.
Mitigation strategies for this vulnerability involve immediate patching of LightDM to versions 1.9.2 or later where the AppArmor profile application for guest accounts has been properly implemented. System administrators should also conduct thorough security audits to ensure that all guest accounts are properly isolated and that AppArmor profiles are correctly applied to all user sessions. Additional defensive measures include implementing strict access controls for guest accounts, monitoring guest session activities, and ensuring that the underlying AppArmor policies are properly configured and enforced. The vulnerability highlights the importance of proper session isolation and access control enforcement in display managers, aligning with ATT&CK technique T1068 Privilege Escalation through the exploitation of insufficient session isolation and access control mechanisms. Organizations should also consider implementing additional monitoring and logging mechanisms to detect unauthorized access attempts through guest accounts, as this vulnerability can be leveraged for both persistent access and further attack escalation.