CVE-2011-4916 in Linux
Summary
by MITRE • 07/13/2022
Linux kernel through 3.1 allows local users to obtain sensitive keystroke information via access to /dev/pts/ and /dev/tty*.
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Analysis
by VulDB Data Team • 08/19/2025
The vulnerability described in CVE-2011-4916 represents a significant security flaw in the Linux kernel affecting versions through 3.1. This issue stems from inadequate access controls within the pseudoterminal and tty subsystems, specifically in how the kernel manages permissions for device files in the /dev/pts/ and /dev/tty* directories. The flaw enables local attackers to gain unauthorized access to sensitive keystroke information that should remain protected from unauthorized users. This vulnerability directly impacts the fundamental security model of Unix-like systems where terminal devices are used for user interaction and input handling.
The technical root cause of this vulnerability lies in the improper implementation of access control mechanisms for pseudoterminal devices and tty interfaces. When users interact with terminal sessions through these device files, the kernel should enforce strict permission controls to prevent unauthorized access to keystroke data. However, in affected kernel versions, the permission checking logic fails to properly validate access requests, allowing local users to read from or write to terminal device files that contain sensitive input data. This represents a violation of the principle of least privilege and creates potential for information disclosure attacks. The vulnerability is classified under CWE-284 Access Control, which specifically addresses inadequate access control mechanisms in software systems.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable more sophisticated attacks. Local users who can access /dev/pts/ and /dev/tty* device files may capture keystrokes from other users, including passwords, commands, and sensitive application data. This capability can lead to privilege escalation attacks when combined with other vulnerabilities, as attackers can capture authentication credentials or sensitive input from other processes. The attack surface is particularly concerning in multi-user environments where users share the same system, as it allows one user to monitor or intercept input from other users. This vulnerability aligns with ATT&CK technique T1056 Input Capture, which focuses on collecting user inputs such as keystrokes from various system components.
Mitigation strategies for CVE-2011-4916 require immediate kernel updates to versions that properly implement access controls for terminal devices. System administrators should prioritize patching affected systems and implementing additional security measures such as restricting access to terminal device files through file system permissions and monitoring for unauthorized access attempts. The solution involves ensuring that proper access control lists are maintained for /dev/pts/ and /dev/tty* directories, preventing local users from accessing terminal device files they should not have access to. Additionally, organizations should implement security monitoring to detect potential exploitation attempts and maintain audit logs of access to terminal devices. This vulnerability underscores the critical importance of proper device file access controls in maintaining system security and user privacy.