CVE-2016-8655 in Linux
Summary
by MITRE • 01/25/2023
Race condition in net/packet/af_packet.c in the Linux kernel through 4.8.12 allows local users to gain privileges or cause a denial of service (use-after-free) by leveraging the CAP_NET_RAW capability to change a socket version, related to the packet_set_ring and packet_setsockopt functions.
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Analysis
by VulDB Data Team • 11/02/2024
The vulnerability described in CVE-2016-8655 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 Linux kernel versions through 4.8.12 and exposes a fundamental weakness in how the kernel handles socket version changes through the CAP_NET_RAW capability. The vulnerability stems from improper synchronization mechanisms during the modification of packet socket ring buffers, creating a window where concurrent operations can lead to unpredictable behavior. The race condition manifests when multiple processes attempt to modify socket parameters simultaneously, particularly when changing socket versions through the packet_set_ring and packet_setsockopt functions. This flaw operates at the kernel level, making it particularly dangerous as it can be exploited by local users who possess the necessary network raw capabilities.
The technical exploitation of this vulnerability involves leveraging the CAP_NET_RAW capability, which is typically required for low-level network packet manipulation. When an attacker with this capability attempts to modify socket parameters, the race condition allows for a use-after-free scenario to occur. The underlying mechanism involves the packet socket's ring buffer management where memory allocation and deallocation occur without proper locking mechanisms. During the transition period between different socket versions, memory that should have been freed becomes accessible to subsequent operations, creating opportunities for both privilege escalation and denial of service attacks. The flaw is categorized under CWE-362, which specifically addresses race conditions, and aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities. The use-after-free condition can be triggered when the packet_set_ring function attempts to reallocate memory while another process is accessing the same memory region, leading to memory corruption that can be exploited to execute arbitrary code with kernel privileges.
The operational impact of CVE-2016-8655 extends beyond simple denial of service to encompass potential full system compromise. Local attackers who can obtain the CAP_NET_RAW capability can leverage this vulnerability to escalate their privileges from user-level to kernel-level execution, effectively gaining complete control over the affected system. The denial of service aspect manifests as system crashes or hangs when the use-after-free condition occurs, potentially leading to persistent availability issues. Systems running vulnerable kernel versions are particularly at risk in environments where users have network raw capabilities, which can occur in various legitimate scenarios such as network monitoring tools, intrusion detection systems, or security research activities. The vulnerability's exploitation requires minimal privileges beyond what is normally expected for network packet manipulation, making it especially dangerous in multi-user environments where such capabilities might be granted to non-privileged users. The impact is further amplified because the vulnerability exists within core network functionality, meaning that exploitation can occur through normal network socket operations without requiring specialized tools or conditions.
Mitigation strategies for CVE-2016-8655 primarily focus on kernel updates and privilege management. The most effective solution involves upgrading to a patched kernel version where the race condition has been addressed through proper synchronization mechanisms. System administrators should prioritize applying security patches from their respective distributions as soon as available, particularly in production environments where the vulnerability could be exploited. Additionally, implementing strict privilege controls can help limit exposure by restricting access to the CAP_NET_RAW capability to only trusted processes and users. The implementation of mandatory access controls through SELinux or AppArmor can provide additional layers of protection by monitoring and restricting socket operations. Network administrators should also consider monitoring for unusual socket operations that might indicate exploitation attempts, particularly around packet socket modifications. The vulnerability serves as a reminder of the importance of proper synchronization in kernel code and highlights the need for comprehensive security testing of core system components. Organizations should also implement regular kernel security assessments to identify similar race conditions and other low-level vulnerabilities that could compromise system integrity. The fix implemented in patched versions typically involves introducing proper mutex locking or other synchronization primitives around the packet_set_ring and packet_setsockopt function calls to prevent concurrent access to shared memory regions during socket parameter modifications.