CVE-2016-9806 in Linux
Summary
by MITRE • 01/25/2023
Race condition in the netlink_dump function in net/netlink/af_netlink.c in the Linux kernel before 4.6.3 allows local users to cause a denial of service (double free) or possibly have unspecified other impact via a crafted application that makes sendmsg system calls, leading to a free operation associated with a new dump that started earlier than anticipated.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-9806 represents a critical race condition within the Linux kernel's netlink networking subsystem, specifically in the netlink_dump function located in net/netlink/af_netlink.c. This flaw exists in kernel versions prior to 4.6.3 and exposes systems to potential denial of service conditions and arbitrary code execution risks. The vulnerability stems from improper synchronization mechanisms during the processing of netlink dump operations, creating a window where concurrent operations can lead to memory corruption. The race condition manifests when a malicious application exploits the timing of sendmsg system calls to manipulate the kernel's internal state during dump processing, ultimately leading to a double free condition that can crash the system or potentially allow privilege escalation.
The technical implementation of this vulnerability involves the improper handling of netlink dump contexts within the kernel's networking layer. When multiple threads or processes attempt to perform netlink dump operations simultaneously, the kernel fails to properly synchronize access to shared memory structures. The race condition occurs during the transition from one dump operation to another, where the kernel frees memory associated with an ongoing dump while a new dump operation begins. This creates a scenario where freed memory is accessed again, resulting in a double free condition that can corrupt the kernel's memory management structures. The flaw is classified under CWE-362, which specifically addresses race conditions in concurrent programming, and aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities.
The operational impact of CVE-2016-9806 extends beyond simple denial of service to potentially enable more severe security consequences. Local attackers with minimal privileges can exploit this vulnerability to crash the kernel, causing system instability and denial of service for legitimate users. In some configurations, particularly those with additional kernel vulnerabilities or specific system setups, the double free condition may allow attackers to manipulate kernel memory layout and potentially achieve privilege escalation. The vulnerability affects systems running Linux kernel versions 4.6.2 and earlier, making it particularly relevant for organizations maintaining older kernel versions or those that have not applied security patches. The exploit requires only local access and can be executed by any user account, making it especially dangerous in multi-user environments where privilege separation is not properly enforced.
Mitigation strategies for CVE-2016-9806 primarily focus on kernel version updates and system hardening measures. The most effective solution involves upgrading to Linux kernel version 4.6.3 or later, where the race condition has been addressed through improved synchronization mechanisms and proper memory management during netlink dump operations. System administrators should prioritize patching affected systems, particularly those running older kernel versions or embedded systems that may not receive regular updates. Additional mitigations include implementing strict access controls to limit local user privileges, monitoring for unusual network activity patterns that might indicate exploitation attempts, and employing kernel hardening techniques such as stack canaries and address space layout randomization. Organizations should also consider implementing intrusion detection systems that can identify suspicious sendmsg operations or abnormal memory access patterns that may indicate exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date kernel versions and proper security practices in preventing exploitation of low-privilege vulnerabilities that can lead to system compromise.