CVE-2021-3835 in zephyrproject-rtos
Summary
by MITRE • 02/08/2022
Buffer overflow in usb device class. Zephyr versions >= v2.6.0 contain Heap-based Buffer Overflow (CWE-122). For more information, see https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-fm6v-8625-99jf
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Analysis
by VulDB Data Team • 02/11/2022
The vulnerability identified as CVE-2021-3835 represents a critical heap-based buffer overflow within the usb device class implementation of the Zephyr real-time operating system. This flaw affects all Zephyr versions starting from v2.6.0 and demonstrates a fundamental weakness in memory management during usb device class processing operations. The vulnerability stems from inadequate bounds checking when handling usb device class data structures, creating an exploitable condition that can be triggered through malicious usb device communication. The affected code path processes usb device class information where insufficient validation allows an attacker to write beyond allocated memory boundaries, potentially leading to arbitrary code execution or system instability.
The technical implementation of this vulnerability manifests as a classic heap-based buffer overflow scenario where the system allocates memory for usb device class data but fails to properly validate input lengths before copying data into allocated buffers. This weakness specifically targets the usb device class processing module within the Zephyr kernel, which handles communication with usb devices and manages device class specific data structures. When a malicious usb device attempts to communicate with a vulnerable Zephyr system, it can craft data that exceeds the allocated buffer size, causing memory corruption that may overwrite adjacent heap allocations or critical system data structures. The vulnerability operates at the kernel level, making it particularly dangerous as it can potentially compromise the entire system integrity.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates opportunities for attackers to execute arbitrary code within the kernel context of affected systems. Systems running vulnerable Zephyr versions that interface with usb devices become susceptible to remote code execution attacks, particularly in environments where untrusted usb devices might be connected. This includes embedded systems, IoT devices, and other platforms that rely on Zephyr for usb device management. The attack surface is broad given the widespread adoption of Zephyr in embedded applications, making this vulnerability particularly concerning for industrial control systems, medical devices, and network infrastructure equipment that may be running affected versions. The exploitation of this vulnerability can lead to complete system compromise, data exfiltration, or denial of service conditions that can persist across system reboots.
Mitigation strategies for CVE-2021-3835 primarily focus on upgrading to patched versions of the Zephyr operating system, specifically those that address the heap-based buffer overflow in usb device class processing. Organizations should prioritize immediate patching of all affected systems running Zephyr versions v2.6.0 through the vulnerable release range. Additionally, implementing runtime protections such as stack canaries, address space layout randomization, and heap memory protection mechanisms can provide defense-in-depth measures. Network segmentation and usb device access controls should be enforced to limit exposure, particularly in critical infrastructure environments. The vulnerability aligns with CWE-122 which specifically addresses heap-based buffer overflow conditions, and can be mapped to ATT&CK technique T1059.007 for execution through kernel-level code injection. Regular security assessments and firmware updates should be implemented as part of ongoing vulnerability management programs to prevent similar issues from arising in the future.