CVE-2016-0723 in Linux
Summary
by MITRE
Race condition in the tty_ioctl function in drivers/tty/tty_io.c in the Linux kernel through 4.4.1 allows local users to obtain sensitive information from kernel memory or cause a denial of service (use-after-free and system crash) by making a TIOCGETD ioctl call during processing of a TIOCSETD ioctl call.
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Analysis
by VulDB Data Team • 07/07/2022
The vulnerability identified as CVE-2016-0723 represents a critical race condition within the Linux kernel's terminal I/O subsystem, specifically affecting the tty_ioctl function in drivers/tty/tty_io.c. This flaw exists in kernel versions through 4.4.1 and creates a dangerous scenario where concurrent operations on terminal devices can lead to unpredictable system behavior. The vulnerability stems from inadequate synchronization mechanisms between the TIOCGETD and TIOCSETD ioctl operations, which are fundamental commands for terminal device control and status retrieval. When a local user executes these operations in rapid succession or during overlapping execution periods, the kernel's internal data structures become vulnerable to improper access patterns that can result in information disclosure or system instability.
The technical implementation of this race condition occurs when the TIOCSETD ioctl call modifies terminal device state while a concurrent TIOCGETD call attempts to read the same kernel memory locations. This timing issue creates a window where the tty layer's internal structures may be in an inconsistent state, leading to potential use-after-free conditions where freed memory blocks are accessed again. The vulnerability is particularly dangerous because it operates at the kernel level, where unauthorized access to kernel memory can expose sensitive system information including credentials, encryption keys, and other confidential data. The race condition manifests through improper locking mechanisms that fail to prevent concurrent access to shared terminal device resources during critical state transitions.
Operationally, this vulnerability provides local attackers with significant capabilities to compromise system integrity and availability. The information disclosure aspect allows attackers to potentially extract sensitive kernel memory contents, which could include cryptographic keys, user credentials, or system configuration details that could be leveraged for further attacks. The denial of service component can cause system crashes or hangs through use-after-free conditions that corrupt kernel data structures or trigger kernel panic states. Attackers can exploit this vulnerability by crafting specific sequences of ioctl calls that create the race condition window, effectively bypassing normal kernel security mechanisms and gaining unauthorized access to kernel memory spaces that should remain protected from user-space access.
Mitigation strategies for CVE-2016-0723 primarily focus on kernel version upgrades to patched releases that address the synchronization issues in the tty subsystem. System administrators should immediately deploy kernel updates from their distribution vendors that contain the necessary fixes for this race condition. Additional protective measures include implementing proper access controls and monitoring for suspicious ioctl activity patterns, particularly in environments where untrusted users have access to terminal devices. The vulnerability aligns with CWE-362, which describes race conditions in concurrent programming, and maps to ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities. Organizations should also consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and kernel module signing to reduce the attack surface and prevent exploitation of similar timing-based vulnerabilities in the terminal I/O subsystem.