CVE-2017-6346 in Linux
Summary
by MITRE
Race condition in net/packet/af_packet.c in the Linux kernel before 4.9.13 allows local users to cause a denial of service (use-after-free) or possibly have unspecified other impact via a multithreaded application that makes PACKET_FANOUT setsockopt system calls.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2017-6346 represents a critical race condition flaw within the Linux kernel's packet socket implementation, specifically in the net/packet/af_packet.c file. This issue affects kernel versions prior to 4.9.13 and demonstrates how improper synchronization mechanisms can lead to severe security implications. The vulnerability manifests when a multithreaded application attempts to manipulate PACKET_FANOUT setsockopt system calls, creating a window where concurrent access to shared kernel resources can result in inconsistent state management. The race condition occurs during the processing of fanout group operations, where multiple threads can simultaneously access and modify the same packet socket structures without adequate locking mechanisms.
The technical exploitation of this vulnerability leverages the inherent timing issues in the kernel's packet socket handling code, particularly around the management of fanout groups and their associated socket references. When multiple threads execute PACKET_FANOUT setsockopt calls concurrently, the kernel fails to properly synchronize access to the underlying data structures that manage fanout group membership. This lack of proper synchronization creates a scenario where one thread might free a socket structure while another thread simultaneously attempts to access it, resulting in a use-after-free condition that can lead to system instability or potential privilege escalation. The flaw resides in the kernel's socket management subsystem and aligns with CWE-362, which specifically addresses race conditions in concurrent programming.
The operational impact of this vulnerability extends beyond simple denial of service, as the use-after-free condition can potentially allow local attackers to execute arbitrary code with kernel privileges. Attackers can craft multithreaded applications that exploit the timing window to cause memory corruption, which may result in system crashes, data loss, or in more sophisticated attack scenarios, privilege escalation to root level access. The vulnerability affects systems that utilize packet socket fanout functionality, which is commonly found in network monitoring tools, intrusion detection systems, and various network analysis applications that rely on the Linux packet socket interface for efficient packet processing and distribution across multiple threads. The attack vector is particularly concerning because it requires only local execution privileges, making it accessible to any user with access to the system.
Mitigation strategies for CVE-2017-6346 primarily focus on kernel version updates, as the most effective solution involves upgrading to Linux kernel version 4.9.13 or later where the race condition has been properly addressed through improved synchronization mechanisms. System administrators should prioritize patching affected systems, particularly those running network monitoring or security applications that might utilize packet socket fanout functionality. Additionally, implementing proper access controls and privilege restrictions can help limit the potential impact of exploitation, though this does not eliminate the vulnerability itself. Organizations should also monitor their network infrastructure for unusual packet processing patterns that might indicate exploitation attempts. The fix implemented in kernel 4.9.13 demonstrates proper adherence to security best practices by introducing appropriate locking mechanisms and ensuring atomic operations when managing fanout group memberships, aligning with ATT&CK technique T1068 which covers privilege escalation through kernel vulnerabilities. Regular security audits and kernel security assessments should be conducted to identify similar race condition vulnerabilities in other kernel subsystems, as this represents a common class of flaws that can lead to significant security implications in operating system components.