CVE-2016-5243 in Linux
Summary
by MITRE
The tipc_nl_compat_link_dump function in net/tipc/netlink_compat.c in the Linux kernel through 4.6.3 does not properly copy a certain string, which allows local users to obtain sensitive information from kernel stack memory by reading a Netlink message.
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Analysis
by VulDB Data Team • 08/25/2022
The vulnerability identified as CVE-2016-5243 resides within the Linux kernel's TIPC (Transparent Inter-Process Communication) subsystem, specifically in the tipc_nl_compat_link_dump function located in net/tipc/netlink_compat.c. This flaw represents a classic information disclosure vulnerability that arises from improper memory handling during the processing of Netlink messages. The TIPC protocol is designed to provide high-performance communication between processes in distributed systems, making it a critical component for kernel-level network operations. The vulnerability manifests when the kernel attempts to serialize and transmit link information through Netlink sockets, creating a scenario where sensitive data from kernel memory space can be inadvertently exposed to unprivileged users.
The technical root cause of this vulnerability stems from a buffer copy operation that fails to properly handle string boundaries within the kernel's memory management. When the tipc_nl_compat_link_dump function processes link dump requests, it attempts to copy string data from kernel space to user space for transmission through Netlink sockets. However, the implementation contains a flaw in how it calculates or copies the string length, resulting in insufficient boundary checking. This improper handling allows a local attacker to craft specific Netlink requests that cause the kernel to copy additional kernel stack memory contents beyond the intended string data. The vulnerability is classified under CWE-125 as an out-of-bounds read, which represents a fundamental flaw in memory safety where the kernel reads beyond allocated memory boundaries. This type of flaw is particularly dangerous because it can expose kernel memory contents including cryptographic keys, passwords, or other sensitive information that should remain protected within kernel space.
The operational impact of CVE-2016-5243 is significant for systems running affected Linux kernel versions, as it provides local attackers with a means to extract sensitive information from kernel memory. Since the vulnerability requires local access to exploit, it does not allow remote code execution or network-based attacks, but it does enable privilege escalation scenarios where an unprivileged user can gain access to kernel memory contents. This information disclosure can be leveraged to gather system intelligence, potentially aiding in more sophisticated attacks such as kernel exploitation or credential harvesting. The vulnerability affects all Linux kernel versions through 4.6.3, making it a widespread concern for organizations maintaining systems with these kernel versions. From an attack framework perspective, this vulnerability aligns with ATT&CK technique T1005 (Data from Local System) and could be used as a reconnaissance step in broader attack chains, particularly in environments where kernel memory exposure might reveal sensitive operational data.
Mitigation strategies for CVE-2016-5243 primarily involve upgrading to patched kernel versions where the memory copy operation has been corrected to properly handle string boundaries and ensure complete data serialization. System administrators should prioritize updating their Linux kernel installations to versions 4.6.4 or later, where the vulnerability has been addressed through proper boundary checking in the tipc_nl_compat_link_dump function. Additionally, organizations should implement monitoring for unusual Netlink message patterns that might indicate exploitation attempts, as well as conduct regular security audits of kernel modules to identify similar memory handling issues. The fix typically involves modifying the string copy operations to ensure that all data copied from kernel memory to user space is properly bounded and that any excess memory content is not inadvertently exposed. Security teams should also consider implementing kernel module hardening measures and restricting local user access to systems where such vulnerabilities might exist, particularly in high-security environments where kernel memory exposure could have severe operational consequences.