CVE-2016-7916 in Android
Summary
by MITRE
Race condition in the environ_read function in fs/proc/base.c in the Linux kernel before 4.5.4 allows local users to obtain sensitive information from kernel memory by reading a /proc/*/environ file during a process-setup time interval in which environment-variable copying is incomplete.
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Analysis
by VulDB Data Team • 09/30/2022
The vulnerability identified as CVE-2016-7916 represents a critical race condition within the Linux kernel's process management subsystem that exposes sensitive kernel memory to local attackers. This flaw exists in the environ_read function located in fs/proc/base.c and affects Linux kernel versions prior to 4.5.4. The vulnerability occurs during the brief window when a process is being set up and its environment variables are being copied from user space to kernel space, creating an exploitable timing gap that adversaries can leverage for information disclosure.
The technical implementation of this vulnerability stems from improper synchronization mechanisms during process creation and environment variable handling. When a process is initialized, the kernel must copy environment variables from the user-space process environment to kernel memory for the /proc//environ interface to function properly. However, this copying operation is not atomic and occurs in multiple steps, creating a temporal window where the kernel memory contains partially copied or uninitialized data. During this interval, local users can repeatedly read the /proc//environ file and potentially capture kernel memory contents, including sensitive information such as stack contents, memory addresses, and other confidential data that should remain protected within kernel space.
This race condition directly maps to CWE-362, which describes a race condition vulnerability where two or more threads or processes access shared resources concurrently, leading to unpredictable behavior and potential security implications. The operational impact of this vulnerability extends beyond simple information disclosure, as the leaked kernel memory can contain sensitive data including cryptographic keys, memory addresses for exploit development, and other confidential information that could be used to facilitate further attacks. The vulnerability affects any local user on the system, making it particularly dangerous as it requires no special privileges beyond standard user access to exploit.
The implications of this vulnerability align with ATT&CK technique T1003.002, which involves OS credential dumping through reading memory, as the leaked information can potentially include credentials or data structures containing authentication information. Attackers could use the leaked memory contents to perform more sophisticated attacks such as kernel exploit development or to gain insights into the system's memory layout for bypassing security mitigations. The vulnerability demonstrates the importance of proper synchronization mechanisms in kernel code, as the lack of adequate locking during critical sections creates opportunities for information leakage that can significantly compromise system security.
Mitigation strategies for this vulnerability require updating to Linux kernel versions 4.5.4 or later, where the race condition has been addressed through proper synchronization mechanisms. System administrators should prioritize patching affected systems and monitor for any exploitation attempts. Additionally, organizations should implement comprehensive monitoring solutions to detect unusual patterns in /proc file access that might indicate exploitation attempts. The fix implemented in the patched kernel versions involves ensuring that environment variable copying operations are properly synchronized, preventing concurrent access to partially initialized kernel memory structures during process setup. Security teams should also consider implementing process monitoring and anomaly detection to identify potential exploitation attempts that could leverage this vulnerability for privilege escalation or information gathering activities.