CVE-2016-2549 in Linux
Summary
by MITRE
sound/core/hrtimer.c in the Linux kernel before 4.4.1 does not prevent recursive callback access, which allows local users to cause a denial of service (deadlock) via a crafted ioctl call.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2549 resides within the Linux kernel's sound subsystem, specifically in the sound/core/hrtimer.c file. This flaw represents a critical design oversight that enables local attackers to exploit recursive callback mechanisms, potentially leading to system-wide denial of service conditions. The vulnerability affects Linux kernel versions prior to 4.4.1, making it a significant concern for systems running older kernel versions where patching may not have been implemented.
The technical implementation of this vulnerability stems from the improper handling of high-resolution timer callbacks within the kernel's audio subsystem. When a crafted ioctl call is executed against audio devices, the kernel's timer handling mechanism can enter a recursive state where callback functions invoke themselves or each other in a manner that creates a deadlock condition. This recursive access pattern bypasses normal kernel synchronization mechanisms and can result in the complete blocking of system resources. The flaw operates at the kernel level, meaning that even though it requires local user access, the impact extends beyond individual processes to potentially compromise entire system operations.
From an operational standpoint, this vulnerability presents a substantial risk to system stability and availability. Local users with access to the system can exploit this flaw to create deadlock conditions that prevent legitimate audio operations from completing, effectively causing a denial of service. The recursive nature of the callback mechanism means that the system may become unresponsive to audio-related operations, potentially affecting other system components that depend on proper timer functionality. This type of vulnerability is particularly concerning in server environments where audio processing might be integral to system operations or where multiple users share the same system resources.
The vulnerability maps to CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) flaws and improper handling of recursive operations. From an ATT&CK framework perspective, this represents a privilege escalation and denial of service technique that leverages kernel-level vulnerabilities. The attack requires local user access but can be executed without elevated privileges, making it particularly dangerous in multi-user environments. The exploitation pattern aligns with techniques described in ATT&CK tactic TA0005 (Defense Evasion) and TA0004 (Privilege Escalation) where attackers can disrupt system operations through kernel manipulation.
Mitigation strategies for CVE-2016-2549 primarily involve upgrading to Linux kernel version 4.4.1 or later where the recursive callback handling has been properly addressed. System administrators should prioritize patching affected systems, particularly those running older kernel versions. Additionally, implementing proper access controls and monitoring for unusual ioctl activity can help detect potential exploitation attempts. The vulnerability demonstrates the importance of proper kernel synchronization mechanisms and recursive function handling in preventing deadlock conditions that can compromise system availability. Organizations should also consider implementing kernel hardening techniques and maintaining up-to-date security patches to protect against similar vulnerabilities in the kernel's audio subsystem and other critical components.