CVE-2016-3955 in Linux
Summary
by MITRE
The usbip_recv_xbuff function in drivers/usb/usbip/usbip_common.c in the Linux kernel before 4.5.3 allows remote attackers to cause a denial of service (out-of-bounds write) or possibly have unspecified other impact via a crafted length value in a USB/IP packet.
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Analysis
by VulDB Data Team • 08/26/2022
The vulnerability identified as CVE-2016-3955 represents a critical out-of-bounds write flaw in the Linux kernel's USB/IP (USB over IP) subsystem affecting versions prior to 4.5.3. This vulnerability resides within the usbip_recv_xbuff function located in drivers/usb/usbip/usbip_common.c, which handles the reception of USB/IP packets. The flaw occurs when the kernel processes USB/IP packets containing malformed length values that exceed the bounds of allocated memory buffers. This type of vulnerability falls under the Common Weakness Enumeration category CWE-121, which encompasses stack-based buffer overflow conditions, and can be classified as a CWE-787 out-of-bounds write due to the improper validation of input parameters. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by remote attackers without requiring local access or authentication.
The technical exploitation of this vulnerability involves sending specially crafted USB/IP packets with invalid length fields that cause the usbip_recv_xbuff function to write data beyond the allocated memory boundaries. When the kernel receives such packets, it fails to properly validate the length parameter before using it to determine buffer boundaries for data reception. This allows attackers to overwrite adjacent memory locations, potentially leading to arbitrary code execution or system crashes that result in denial of service conditions. The vulnerability demonstrates characteristics consistent with the attack pattern described in ATT&CK technique T1059.007 for command and scripting interpreter, as it can enable privilege escalation through kernel memory corruption. The impact extends beyond simple denial of service as the out-of-bounds write can corrupt critical kernel data structures, leading to system instability or potential privilege escalation.
The operational impact of CVE-2016-3955 is significant for systems running affected Linux kernel versions, particularly those operating as USB/IP servers or hosts that accept remote USB connections. Systems that expose USB devices over IP networks, such as those using USB/IP for remote device access or virtualization environments, become vulnerable to remote exploitation. The vulnerability affects both the server and client components of the USB/IP implementation, meaning that any system processing USB/IP packets could be compromised. Organizations using embedded systems, industrial control systems, or virtualization platforms that rely on USB/IP functionality are particularly at risk. The vulnerability can be exploited by attackers who can send malicious USB/IP packets to the target system, potentially leading to complete system compromise. The nature of the flaw means that exploitation does not require elevated privileges and can be performed remotely, making it a serious concern for networked systems. Additionally, the vulnerability can be leveraged in combination with other attack vectors to achieve more sophisticated exploits, as demonstrated by the ATT&CK framework's approach to privilege escalation techniques.
Mitigation strategies for CVE-2016-3955 primarily involve upgrading to Linux kernel versions 4.5.3 or later where the vulnerability has been patched. The fix implemented by the kernel maintainers includes proper validation of length parameters before memory allocation and bounds checking to prevent out-of-bounds writes. System administrators should also consider implementing network segmentation to limit access to USB/IP services and disable USB/IP functionality when not required. Network-based mitigations include firewall rules that restrict access to USB/IP ports and services, as well as intrusion detection systems that can identify and block suspicious USB/IP packet patterns. Organizations should also conduct regular vulnerability assessments to identify systems running affected kernel versions and ensure that all USB/IP related services are properly configured with appropriate access controls. The patch addresses the root cause by implementing proper input validation and memory boundary checking, which aligns with security best practices outlined in the CWE guidelines for preventing buffer overflow vulnerabilities. Additionally, implementing kernel hardening measures such as stack canaries and address space layout randomization can provide additional protection against exploitation attempts.