CVE-2016-3951 in Android
Summary
by MITRE
Double free vulnerability in drivers/net/usb/cdc_ncm.c in the Linux kernel before 4.5 allows physically proximate attackers to cause a denial of service (system crash) or possibly have unspecified other impact by inserting a USB device with an invalid USB descriptor.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-3951 represents a critical double free condition within the Linux kernel's USB network control model driver implementation. This flaw exists in the cdc_ncm.c file located in the drivers/net/usb/ directory of the kernel source tree, affecting all versions prior to 4.5. The vulnerability specifically targets the handling of USB descriptors during device enumeration processes, creating a scenario where memory management operations can be exploited through physical proximity attacks. The double free condition occurs when the kernel's USB network driver fails to properly validate USB descriptor structures, leading to memory allocation and deallocation sequences that can be manipulated by malicious USB devices.
The technical exploitation of this vulnerability requires an attacker to physically present a malicious USB device to a target system, leveraging the USB descriptor parsing functionality within the kernel's USB subsystem. When the kernel processes the invalid USB descriptor provided by the malicious device, it triggers the double free condition in the cdc_ncm driver code. This memory management error manifests as the kernel attempting to free the same memory block twice, which can result in heap corruption and unpredictable system behavior. The vulnerability falls under CWE-415, which specifically addresses double free conditions in memory management, and can be classified as a type of heap-based buffer overflow that compromises the kernel's memory integrity.
From an operational perspective, the impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attacks. The system crash resulting from the double free condition can be leveraged to cause persistent availability issues, while the underlying memory corruption may provide opportunities for privilege escalation or information disclosure. The physical proximity requirement limits the attack surface but does not eliminate the threat, as USB devices can be easily concealed and deployed in targeted environments. The vulnerability aligns with ATT&CK technique T1059.005, which involves the use of USB devices for malicious purposes, and can be categorized under the broader category of physical attack vectors that compromise system integrity.
Mitigation strategies for CVE-2016-3951 primarily focus on kernel version updates, with the most effective solution being the deployment of Linux kernel versions 4.5 and later where the double free condition has been addressed through proper descriptor validation and memory management. System administrators should also implement USB device whitelisting policies and disable unnecessary USB functionality on systems where physical security cannot be guaranteed. Additional protective measures include monitoring for unusual USB device enumeration patterns and implementing kernel lockdown features that restrict kernel memory access. The vulnerability demonstrates the importance of proper input validation in kernel space and highlights the need for comprehensive security testing of USB device drivers. Organizations should conduct regular security assessments of their kernel versions and ensure that all systems are updated to patched versions to prevent exploitation of this and similar memory corruption vulnerabilities.