CVE-2016-10200 in Linux
Summary
by MITRE
Race condition in the L2TPv3 IP Encapsulation feature in the Linux kernel before 4.8.14 allows local users to gain privileges or cause a denial of service (use-after-free) by making multiple bind system calls without properly ascertaining whether a socket has the SOCK_ZAPPED status, related to net/l2tp/l2tp_ip.c and net/l2tp/l2tp_ip6.c.
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Analysis
by VulDB Data Team • 09/04/2020
The vulnerability CVE-2016-10200 represents a critical race condition affecting the Layer 2 Tunneling Protocol version 3 IP Encapsulation implementation within the Linux kernel. This flaw exists in the net/l2tp/l2tp_ip.c and net/l2tp/l2tp_ip6.c kernel source files and impacts versions prior to 4.8.14. The vulnerability stems from improper handling of socket states during concurrent bind operations, creating a window where malicious local users can exploit the system to either escalate privileges or induce denial of service conditions. The race condition specifically occurs when multiple bind system calls are made without adequate verification of socket status, particularly the SOCK_ZAPPED flag that indicates whether a socket has been properly initialized.
The technical exploitation of this vulnerability relies on a use-after-free condition that manifests when the kernel fails to properly synchronize access to L2TPv3 sockets during concurrent operations. When multiple threads or processes attempt to bind to L2TPv3 sockets simultaneously, the kernel's socket management logic does not adequately prevent race conditions that could result in dangling pointers or memory corruption. This condition allows attackers to manipulate the socket state in such a way that subsequent operations on the socket structure can access freed memory locations, potentially leading to arbitrary code execution with kernel privileges. The vulnerability is classified under CWE-362 as a Concurrent Execution using Shared Resource with Unprotected Race Condition, and it aligns with ATT&CK technique T1068 which covers Local Privilege Escalation through kernel exploits.
The operational impact of this vulnerability extends beyond simple privilege escalation to include potential system instability and complete denial of service scenarios. Local users with minimal privileges can leverage this race condition to either elevate their privileges to root level access or to crash the kernel through memory corruption. The use-after-free condition creates an unpredictable environment where the kernel's memory management can be manipulated to execute malicious code, making it particularly dangerous in multi-user environments. The vulnerability's exploitation requires careful timing and concurrent access patterns, but once successful, it provides attackers with persistent access to the compromised system. Organizations running affected kernel versions face significant risk as this vulnerability can be exploited without requiring special privileges beyond basic user access, and the attack surface includes any system with L2TPv3 functionality enabled. The flaw demonstrates the complexity of kernel-level race condition management and highlights the importance of proper synchronization mechanisms in network protocol implementations.
Mitigation strategies for CVE-2016-10200 primarily involve upgrading to kernel versions 4.8.14 or later where the race condition has been addressed through proper socket state management and synchronization. System administrators should also implement monitoring for unusual bind operations on L2TPv3 sockets and consider disabling L2TPv3 functionality if it is not required for system operations. Additional protective measures include implementing proper access controls and privilege separation to limit the potential impact of successful exploitation. The fix implemented in kernel versions 4.8.14 addresses the root cause by ensuring proper locking mechanisms and socket state validation during concurrent bind operations, preventing the race condition that previously allowed for use-after-free scenarios. Organizations should also conduct vulnerability assessments to identify systems running affected kernel versions and prioritize patching efforts based on risk exposure and system criticality.