CVE-2016-7917 in Android
Summary
by MITRE
The nfnetlink_rcv_batch function in net/netfilter/nfnetlink.c in the Linux kernel before 4.5 does not check whether a batch message's length field is large enough, which allows local users to obtain sensitive information from kernel memory or cause a denial of service (infinite loop or out-of-bounds read) by leveraging the CAP_NET_ADMIN capability.
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Analysis
by VulDB Data Team • 09/30/2022
The vulnerability identified as CVE-2016-7917 resides within the Linux kernel's netfilter subsystem, specifically in the nfnetlink_rcv_batch function located at net/netfilter/nfnetlink.c. This flaw represents a critical security issue that affects Linux kernel versions prior to 4.5, where the function fails to properly validate the length field of batch messages. The vulnerability is particularly concerning because it can be exploited by locally authenticated users who possess the CAP_NET_ADMIN capability, which is typically granted to network administrators or processes requiring elevated network permissions. The absence of proper bounds checking on the batch message length field creates a pathway for malicious actors to manipulate kernel memory structures through crafted input data.
The technical nature of this vulnerability stems from insufficient input validation within the kernel's netfilter processing pipeline. When the nfnetlink_rcv_batch function receives a batch message, it does not verify that the specified length field corresponds to a valid message size that would prevent buffer overflows or out-of-bounds memory access. This allows attackers to construct specially crafted batch messages with manipulated length fields that can cause the kernel to read beyond allocated memory boundaries or enter infinite loop conditions. The vulnerability manifests as either information disclosure through kernel memory leaks or denial of service conditions that can crash the system or render it unresponsive. The flaw aligns with CWE-129, which addresses improper validation of length fields, and represents a classic example of an out-of-bounds read vulnerability in kernel space.
The operational impact of CVE-2016-7917 extends beyond simple denial of service scenarios, as it can potentially lead to information disclosure that exposes sensitive kernel memory contents to local attackers. This information leakage could reveal kernel addresses, configuration details, or other confidential data that might aid in further exploitation attempts. The vulnerability affects systems running Linux kernel versions before 4.5, making it particularly relevant for organizations maintaining older kernel versions or those that have not yet applied the necessary security patches. The requirement for CAP_NET_ADMIN capability means that exploitation is limited to users who already have network administration privileges, but this access level is often available to system administrators, services, or applications that require network filtering capabilities. The vulnerability demonstrates how seemingly minor input validation gaps can create significant security risks within kernel space, where improper memory handling can compromise entire system integrity.
Mitigation strategies for CVE-2016-7917 primarily involve upgrading to Linux kernel version 4.5 or later, where the vulnerability has been addressed through proper bounds checking implementation. System administrators should prioritize patching affected systems, particularly those running older kernel versions that may be exposed to local privilege escalation attempts. Additionally, organizations should implement strict access controls to limit the number of users or processes with CAP_NET_ADMIN capability, as this reduces the attack surface for exploitation. The vulnerability highlights the importance of comprehensive input validation in kernel space code and underscores the need for thorough security reviews of system call interfaces that handle batch processing operations. Security monitoring should include detection of abnormal network filtering activities that might indicate exploitation attempts, while also ensuring that all kernel components undergo regular security assessments to identify similar validation gaps that could lead to privilege escalation or information disclosure vulnerabilities. This vulnerability serves as a reminder of the critical importance of kernel security and the potential for local privilege escalation through seemingly minor implementation flaws in core system components.