CVE-2021-47474 in Linux
Summary
by MITRE • 05/22/2024
In the Linux kernel, the following vulnerability has been resolved:
comedi: vmk80xx: fix bulk-buffer overflow
The driver is using endpoint-sized buffers but must not assume that the tx and rx buffers are of equal size or a malicious device could overflow the slab-allocated receive buffer when doing bulk transfers.
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Analysis
by VulDB Data Team • 11/22/2025
The vulnerability identified as CVE-2021-47474 affects the Linux kernel's comedi subsystem, specifically the vmk80xx driver implementation. This driver interfaces with certain USB-based data acquisition devices and is part of the broader Comedi framework designed to provide unified access to various data acquisition hardware. The flaw resides in how the driver manages memory buffers during bulk data transfers, creating a potential pathway for buffer overflow conditions that could be exploited by malicious devices.
The technical root cause involves improper buffer size assumptions within the driver's implementation. The vmk80xx driver utilizes endpoint-sized buffers for communication but fails to validate that transmit and receive buffers maintain equal sizes. This design assumption creates a critical security gap where a malicious device could manipulate data transfers to overflow the slab-allocated receive buffer. The vulnerability stems from a lack of proper bounds checking and buffer size validation during bulk transfer operations, particularly when handling data from USB endpoints with varying buffer capacities.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a classic buffer overflow condition that could lead to arbitrary code execution or system instability. When a malicious device attempts to send more data than the allocated receive buffer can accommodate, the overflow could overwrite adjacent memory regions, potentially corrupting kernel data structures or enabling privilege escalation attacks. This risk is particularly concerning given that the comedi subsystem operates at kernel level and handles hardware communication directly, making it a prime target for exploitation.
Security researchers categorize this vulnerability under CWE-121, which addresses stack buffer overflow conditions, though the specific implementation involves heap-based buffer overflows due to slab allocation patterns. The vulnerability aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel exploits, as exploitation could potentially allow attackers to gain elevated system privileges. Mitigation strategies should focus on implementing proper buffer size validation and ensuring that all bulk transfer operations enforce strict bounds checking regardless of endpoint characteristics. The fix involves modifying the driver to allocate appropriately sized buffers and validate transfer sizes before processing data, preventing the overflow condition that could be exploited by malicious hardware devices.