CVE-2013-1940 in X Window System
Summary
by MITRE
X.Org X server before 1.13.4 and 1.4.x before 1.14.1 does not properly restrict access to input events when adding a new hot-plug device, which might allow physically proximate attackers to obtain sensitive information, as demonstrated by reading passwords from a tty.
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Analysis
by VulDB Data Team • 05/10/2021
The vulnerability identified as CVE-2013-1940 affects the X.Org X server implementation across multiple versions including those before 1.13.4 and 1.4.x before 1.14.1. This represents a critical security flaw in the X Window System that governs graphical user interfaces on Unix-like operating systems. The vulnerability specifically manifests during the hot-plug device addition process, where the system fails to properly enforce access controls on input events. This design flaw creates a window of opportunity for attackers who are physically proximate to the target system to exploit the system's security boundaries. The implications extend beyond simple privilege escalation as they fundamentally compromise the integrity of input handling mechanisms that are critical to system security. The X server's handling of input events during device hot-plug operations becomes a vector for information leakage that could expose sensitive data.
The technical root cause of this vulnerability lies in the improper access control implementation within the X server's input event handling subsystem. When a new device is added through hot-plug mechanisms, the system should enforce strict access controls to prevent unauthorized observation of input events. However, the flawed implementation allows unauthorized processes or users to intercept and potentially read input events that should be restricted to specific privileged contexts. This misconfiguration creates a scenario where input events from keyboards or other input devices can be observed by processes that do not have legitimate access rights to such information. The vulnerability operates at a fundamental level of the X server's security model, where the boundary between trusted and untrusted input processing is improperly enforced.
The operational impact of this vulnerability is particularly concerning as it demonstrates a real-world exploitability scenario involving physical proximity attacks. An attacker positioned near a target system can potentially capture sensitive information such as passwords typed on a terminal through the tty interface. This attack vector bypasses traditional network-based security measures and exploits the local system's trust model. The vulnerability essentially allows for keystroke logging without requiring network access or complex exploitation techniques. The attack surface expands to include any system where hot-plug devices are frequently added or removed, making it particularly dangerous in shared or public computing environments where physical access cannot be easily controlled.
The security implications of this vulnerability align with CWE-284, which addresses improper access control in software systems. This classification specifically addresses scenarios where systems fail to properly enforce access restrictions on resources that should be protected from unauthorized access. The attack pattern also correlates with ATT&CK technique T1056.001, which covers input injection attacks, particularly those involving physical proximity and local system access. Organizations using affected X server versions face significant risk exposure where attackers can leverage this vulnerability to gain unauthorized access to sensitive information without requiring sophisticated attack tools or extensive system compromise. The vulnerability essentially undermines the fundamental security assumptions of local input handling and creates persistent exposure windows during device management operations.
Mitigation strategies for this vulnerability require immediate patching of affected X server versions to the corrected releases. System administrators should prioritize updating their X server implementations to versions 1.13.4 or later for the 1.13.x series, and 1.14.1 or later for the 1.4.x series. Additionally, organizations should implement physical security measures to prevent unauthorized access to systems where this vulnerability exists. Network segmentation and access control policies should be reviewed to ensure that local input events are properly isolated from unauthorized processes. Monitoring systems should be enhanced to detect unusual input event processing patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper access control implementation in system-level components and the critical need for thorough security review of device management and input handling functions within graphical server implementations.