CVE-2005-0839 in Linux
Summary
by MITRE
linux kernel 2.6 before 2.6.11 does not restrict access to the n_mouse line discipline for a tty which allows local users to gain privileges by injecting mouse or keyboard events into other user sessions.
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Analysis
by VulDB Data Team • 06/11/2019
The vulnerability described in CVE-2005-0839 represents a significant privilege escalation flaw within the linux kernel version 2.6.11 and earlier releases. This issue stems from insufficient access controls within the n_mouse line discipline implementation, which is responsible for handling mouse and keyboard input through terminal devices. The vulnerability specifically affects systems where multiple users share terminal sessions or where console access is available, creating a pathway for malicious local users to exploit the system's input handling mechanisms.
The technical flaw resides in the kernel's failure to properly enforce access restrictions on the n_mouse line discipline, which typically manages input from serial mouse devices connected to tty lines. When a local user gains access to a terminal session, they can potentially inject mouse or keyboard events into other user sessions through this poorly protected interface. This occurs because the kernel does not adequately validate or authenticate input sources before processing events through the n_mouse line discipline, allowing unauthorized users to manipulate the input stream of other active sessions.
The operational impact of this vulnerability is severe as it enables local privilege escalation attacks that can compromise user sessions and potentially escalate to root privileges. An attacker with access to a low-privilege account can leverage this vulnerability to inject malicious input events that might trigger unintended system behavior or allow them to execute commands in the context of other users. This type of attack can be particularly dangerous in multi-user environments such as shared servers, terminal servers, or systems where users need to maintain separate session contexts. The vulnerability essentially undermines the fundamental security model of user isolation within the kernel's terminal handling mechanisms.
This vulnerability maps to CWE-284 Access Control, specifically addressing insufficient access control mechanisms in kernel-level input handling components. The attack vector aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities, and T1548.001, covering abuse of privileges through local escalation techniques. The flaw demonstrates a classic case of inadequate input validation and privilege separation in kernel space, where the system fails to properly isolate user sessions through the tty subsystem.
Mitigation strategies for this vulnerability include upgrading to linux kernel version 2.6.11 or later, which contains the necessary patches to properly restrict access to the n_mouse line discipline. System administrators should also implement proper access controls and monitoring of terminal sessions to detect unauthorized input injection attempts. Additionally, disabling unnecessary mouse and keyboard input handling for tty devices when not required, and implementing proper user session isolation mechanisms can reduce the attack surface. Organizations should also consider implementing kernel hardening measures such as grsecurity or similar security modules that provide additional protections against such kernel-level privilege escalation attacks. Regular security audits of kernel configurations and input handling mechanisms should be conducted to ensure that similar vulnerabilities are not present in other system components.