CVE-2016-2548 in Linux
Summary
by MITRE
sound/core/timer.c in the Linux kernel before 4.4.1 retains certain linked lists after a close or stop action, which allows local users to cause a denial of service (system crash) via a crafted ioctl call, related to the (1) snd_timer_close and (2) _snd_timer_stop functions.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-2548 resides within the Linux kernel's sound subsystem, specifically in the sound/core/timer.c file. This flaw represents a memory management issue that affects kernel versions prior to 4.4.1, creating a persistent security risk for systems utilizing the Advanced Linux Sound Architecture. The vulnerability stems from improper handling of linked list data structures within the audio timer subsystem, where certain list nodes are not properly removed from memory upon closure or stopping of timer operations.
The technical implementation of this vulnerability involves the snd_timer_close and _snd_timer_stop functions which are responsible for managing audio timer resources in the kernel. When these functions are invoked through crafted ioctl system calls, they fail to completely dismantle the linked list structures that maintain timer state information. This memory leak occurs because the kernel does not properly traverse and free all nodes within the linked list, leaving references to freed memory that can be exploited by malicious local users. The flaw is particularly dangerous because it operates at the kernel level, allowing attackers with local access to potentially trigger system crashes through carefully constructed audio timer operations.
The operational impact of CVE-2016-2548 manifests as a local denial of service condition that can result in complete system crashes or reboot cycles. Attackers with local user privileges can exploit this vulnerability by making specific ioctl calls that trigger the improper linked list cleanup behavior, causing the kernel to encounter dangling pointers or corrupted memory structures during subsequent operations. This vulnerability directly relates to CWE-457, which addresses the use of uninitialized memory, and CWE-121, concerning stack-based buffer overflow conditions that can lead to system instability. The attack vector requires local system access and does not involve network exposure, making it a local privilege escalation risk that can be particularly problematic in multi-user environments.
Mitigation strategies for this vulnerability require immediate kernel version updates to 4.4.1 or later, where the linked list management has been properly corrected. System administrators should prioritize patching affected systems and implement monitoring for unusual audio subsystem activity that might indicate exploitation attempts. Additionally, organizations should consider implementing kernel lockdown mechanisms and restricting local user access to audio devices where possible. The remediation aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities, and addresses the broader category of privilege escalation methods that target kernel memory management flaws. Regular security assessments should include verification of kernel versions and proper implementation of security patches to prevent exploitation of similar memory management vulnerabilities that may exist in other subsystems.