CVE-2016-3137 in Linux
Summary
by MITRE
drivers/usb/serial/cypress_m8.c in the Linux kernel before 4.5.1 allows physically proximate attackers to cause a denial of service (NULL pointer dereference and system crash) via a USB device without both an interrupt-in and an interrupt-out endpoint descriptor, related to the cypress_generic_port_probe and cypress_open functions.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability identified as CVE-2016-3137 represents a critical NULL pointer dereference flaw within the Linux kernel's USB serial driver subsystem, specifically affecting the cypress_m8.c module. This issue exists in kernel versions prior to 4.5.1 and demonstrates a classic buffer overflow condition that can be exploited through physical proximity attacks. The vulnerability stems from inadequate input validation within the USB device enumeration process, where the kernel fails to properly handle USB devices that lack both interrupt-in and interrupt-out endpoint descriptors. This flaw falls under the Common Weakness Enumeration category of CWE-476 which encompasses NULL pointer dereference vulnerabilities, making it particularly dangerous as it can lead to complete system compromise through denial of service attacks.
The technical execution of this vulnerability occurs during the USB device probe and open operations within the Cypress USB serial driver. When a malicious USB device is connected that lacks both interrupt endpoints, the cypress_generic_port_probe function attempts to access memory locations that have not been properly initialized, leading to a NULL pointer dereference. The cypress_open function subsequently triggers the system crash when it tries to process the incomplete USB device configuration. This attack vector is particularly concerning because it requires only physical proximity to the target system, making it accessible to attackers who can physically interact with the device, such as in public spaces or shared work environments. The vulnerability demonstrates a clear violation of the principle of least privilege and proper input validation that should be enforced at all levels of system software.
The operational impact of CVE-2016-3137 extends beyond simple denial of service to potentially enable more sophisticated attack scenarios. While the immediate effect is a system crash and reboot, this vulnerability can be leveraged as a stepping stone for further exploitation attempts. Attackers can repeatedly connect and disconnect malicious USB devices to create persistent denial of service conditions, effectively rendering the system unusable for legitimate users. The attack surface is particularly broad given that USB ports are ubiquitous on modern computing devices, making this vulnerability exploitable across numerous device types including laptops, desktops, servers, and embedded systems. From an operational security perspective, this vulnerability directly impacts the availability and reliability of systems, potentially causing business disruption and data loss. The issue aligns with ATT&CK technique T1059.001 which involves the use of command and scripting interpreters, as the compromised system becomes vulnerable to further exploitation once the initial denial of service occurs.
Mitigation strategies for CVE-2016-3137 primarily focus on kernel version updates and system hardening measures. The most effective immediate solution is upgrading to Linux kernel version 4.5.1 or later, where the vulnerability has been patched through proper input validation and null pointer checks. System administrators should also implement USB device whitelisting policies to restrict which devices can connect to critical systems, particularly in high-security environments. Additional mitigations include disabling USB ports when not in use, implementing USB device authorization controls, and monitoring for unusual USB device connections. The vulnerability highlights the importance of proper kernel security testing and the need for robust input validation in device driver code, as outlined in the Secure Coding practices recommended by the CERT/CC. Organizations should also consider implementing USB device management solutions that can detect and prevent the connection of potentially malicious USB devices, thereby reducing the attack surface and preventing exploitation of this and similar vulnerabilities.