CVE-2016-4569 in Android
Summary
by MITRE
The snd_timer_user_params function in sound/core/timer.c in the Linux kernel through 4.6 does not initialize a certain data structure, which allows local users to obtain sensitive information from kernel stack memory via crafted use of the ALSA timer interface.
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Analysis
by VulDB Data Team • 09/12/2022
The vulnerability identified as CVE-2016-4569 represents a critical information disclosure flaw within the Linux kernel's Advanced Linux Sound Architecture implementation. This issue affects kernel versions through 4.6 and stems from improper initialization of a data structure within the snd_timer_user_params function located in sound/core/timer.c. The flaw specifically impacts the ALSA timer interface, which is a fundamental component of the Linux audio subsystem responsible for managing timing operations in sound devices. When users interact with the ALSA timer interface through crafted system calls, the uninitialized data structure exposes kernel memory contents to unauthorized access.
The technical nature of this vulnerability aligns with CWE-457, which describes "Use of Uninitialized Variable" in software development practices. This particular implementation flaw occurs because the snd_timer_user_params function fails to properly initialize memory before using it, creating a scenario where sensitive kernel stack data remains accessible to local users. The vulnerability exists at the kernel level, making it particularly dangerous as it operates within the most privileged execution context of the operating system. Attackers can exploit this by constructing specific ALSA timer interface calls that trigger the function with uninitialized memory, thereby allowing them to read kernel stack contents that may contain sensitive information such as cryptographic keys, passwords, or other confidential data.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides local attackers with potential access to kernel memory that could contain credentials, encryption keys, or other sensitive data structures. This represents a significant security risk in multi-user environments where local access might be obtained through various attack vectors such as compromised user accounts, privilege escalation attempts, or social engineering tactics. The vulnerability affects any system running Linux kernel versions 4.6 or earlier that have ALSA audio support enabled, which includes virtually all desktop and server distributions. From an attack perspective, this vulnerability fits within the ATT&CK technique T1005, which involves "Data from Local System" and can be leveraged to gather sensitive information that might aid in further exploitation attempts.
Mitigation strategies for CVE-2016-4569 primarily focus on kernel updates and system hardening measures. The most effective solution involves upgrading to Linux kernel versions 4.7 or later, where the vulnerability has been patched through proper initialization of the affected data structure. System administrators should also implement proper access controls and monitor for suspicious ALSA timer interface usage patterns. Additionally, organizations should consider disabling unnecessary audio services and restricting local user access to audio subsystem interfaces where possible. The patch for this vulnerability specifically addresses the uninitialized variable issue by ensuring proper memory initialization before data structure usage, which prevents the leakage of kernel stack contents to unprivileged users. Security monitoring should include detection of unusual ALSA timer interface calls that might indicate exploitation attempts, and system administrators should maintain current kernel versions to protect against similar vulnerabilities.