CVE-2016-2543 in Linux
Summary
by MITRE
The snd_seq_ioctl_remove_events function in sound/core/seq/seq_clientmgr.c in the Linux kernel before 4.4.1 does not verify FIFO assignment before proceeding with FIFO clearing, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) via a crafted ioctl call.
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability identified as CVE-2016-2543 resides within the Linux kernel's sound subsystem, specifically in the sequencer client management component. This flaw affects versions prior to 4.4.1 and represents a classic case of improper input validation that can lead to system instability. The vulnerability is classified under CWE-476 which deals with null pointer dereference issues, making it particularly dangerous as it can cause kernel panics and system crashes. The affected function snd_seq_ioctl_remove_events operates within the sound/core/seq/seq_clientmgr.c file, which manages sequencer client operations and FIFO (First In First Out) buffer handling for audio event processing.
The technical exploitation of this vulnerability occurs when a local attacker crafts a malicious ioctl (input/output control) call that triggers the remove_events function without proper FIFO assignment verification. The function fails to validate whether a FIFO has been properly assigned before attempting to clear it, leading to a scenario where a NULL pointer dereference occurs. This type of error manifests as an OOPS (Oops) message in kernel logs, indicating a kernel bug that results in system instability. The absence of proper validation creates a path where the kernel attempts to access memory locations that have not been initialized or allocated, causing the kernel to crash and potentially resulting in a complete system denial of service.
The operational impact of this vulnerability extends beyond simple system crashes as it provides a reliable method for local privilege escalation attacks. Since the vulnerability requires only local user access to exploit, it can be leveraged by malicious users or processes running with standard user privileges to disrupt system operations. This makes it particularly concerning in multi-user environments where untrusted users might be present. The vulnerability can be exploited to create persistent denial of service conditions that could affect audio services, system stability, and potentially other applications that rely on the kernel's audio subsystem for proper operation. From an attack perspective, this vulnerability aligns with ATT&CK technique T1068 which involves local privilege escalation through kernel exploits.
Mitigation strategies for CVE-2016-2543 primarily focus on upgrading to kernel versions 4.4.1 or later where the vulnerability has been patched. The fix implemented by the Linux kernel developers involves adding proper validation checks to ensure FIFO assignments are verified before attempting any clearing operations. System administrators should also implement monitoring solutions to detect unusual ioctl activity patterns that might indicate exploitation attempts. Additional defensive measures include restricting local user access to audio subsystem interfaces when possible and implementing proper system hardening practices that limit the attack surface. The vulnerability demonstrates the importance of proper kernel input validation and the critical nature of maintaining up-to-date system software to prevent exploitation of known vulnerabilities. Organizations should prioritize patch management processes to ensure all systems receive timely security updates, particularly for kernel-level vulnerabilities that can provide attackers with system control.