CVE-2016-20022 in Linux
Summary
by MITRE • 06/28/2024
In the Linux kernel before 4.8, usb_parse_endpoint in drivers/usb/core/config.c does not validate the wMaxPacketSize field of an endpoint descriptor. NOTE: This vulnerability only affects products that are no longer supported by the supplier.
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Analysis
by VulDB Data Team • 08/17/2025
The vulnerability identified as CVE-2016-20022 represents a critical flaw in the Linux kernel's USB subsystem that existed prior to version 4.8. This issue resides within the usb_parse_endpoint function located in drivers/usb/core/config.c, where insufficient validation of the wMaxPacketSize field in USB endpoint descriptors creates a potential security risk. The vulnerability specifically targets the parsing logic that handles USB configuration descriptors, which are essential for proper device enumeration and communication within the USB framework. The wMaxPacketSize field contains crucial information about the maximum packet size that an endpoint can handle, making it a critical parameter for USB device operation and system stability.
The technical flaw stems from the absence of proper bounds checking and validation for the wMaxPacketSize value during USB endpoint descriptor parsing. This field typically contains a 16-bit value that specifies the maximum packet size in bytes for data transfers to or from the endpoint. When this field is not properly validated, malicious or malformed USB devices could potentially craft endpoint descriptors with invalid wMaxPacketSize values that exceed normal operating parameters. Such invalid values could lead to buffer overflows, memory corruption, or other exploitable conditions within the kernel's USB subsystem. According to CWE classification, this vulnerability aligns with CWE-129: Improper Validation of Array Index, as the lack of validation allows for potentially dangerous values to be processed without proper bounds checking.
The operational impact of this vulnerability extends beyond simple system instability, as it could potentially be exploited to execute arbitrary code within the kernel context. An attacker with physical access to a vulnerable system could connect a malicious USB device that presents malformed endpoint descriptors, potentially triggering memory corruption issues that could be leveraged for privilege escalation or system compromise. The attack vector requires physical presence or the ability to connect unauthorized USB devices, which aligns with ATT&CK technique T1059.001 for executing commands and T1021.002 for remote services. However, the vulnerability's limited scope means it primarily affects systems where USB devices are frequently connected and where proper input validation is not enforced, making it particularly concerning in environments where untrusted USB devices might be encountered.
While the vulnerability description notes that affected products are no longer supported by suppliers, the underlying principles of this flaw remain relevant for understanding kernel security vulnerabilities and the importance of proper input validation in system-level code. The issue demonstrates how seemingly minor validation gaps in kernel subsystems can create significant security risks, particularly in USB frameworks where devices can present arbitrary descriptors. Organizations should consider implementing USB device whitelisting policies, disabling unnecessary USB functionality, and ensuring that systems are running supported kernel versions where possible. The vulnerability also underscores the importance of maintaining up-to-date security patches and understanding that even unsupported systems may still contain exploitable flaws that could be relevant in specific threat scenarios. The root cause highlights the necessity of comprehensive input validation in kernel drivers and serves as a reminder that USB subsystems require robust sanitization of all incoming descriptor data to prevent exploitation through malformed device configurations.