CVE-2023-53840 in Linux
Summary
by MITRE • 12/09/2025
In the Linux kernel, the following vulnerability has been resolved:
usb: early: xhci-dbc: Fix a potential out-of-bound memory access
If xdbc_bulk_write() fails, the values in 'buf' can be anything. So the string is not guaranteed to be NULL terminated when xdbc_trace() is called.
Reserve an extra byte, which will be zeroed automatically because 'buf' is a static variable, in order to avoid troubles, should it happen.
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Analysis
by VulDB Data Team • 03/30/2026
The vulnerability identified as CVE-2023-53840 represents a critical out-of-bounds memory access issue within the Linux kernel's USB subsystem, specifically affecting the xhci-dbc driver component. This flaw exists in the handling of USB debug trace functionality where the xdbc_bulk_write() function may fail during data transmission operations. When this failure occurs, the buffer variable 'buf' contains unpredictable data values that are not guaranteed to be null-terminated, creating a dangerous condition that could lead to memory corruption and system instability.
The technical implementation of this vulnerability stems from improper buffer management within the USB debug trace mechanism. The xhci-dbc driver utilizes a static buffer variable 'buf' to store debug information for USB transactions, but when xdbc_bulk_write() fails, the buffer contents become undefined and potentially contain arbitrary data. The function xdbc_trace() subsequently processes this buffer without ensuring proper null termination, creating a scenario where memory access operations could extend beyond the allocated buffer boundaries. This type of flaw falls under the CWE-121 CWE category for buffer overflow conditions, specifically involving stack-based buffer overflows that can lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could enable attackers to exploit the out-of-bounds access for privilege escalation or system compromise. The xhci-dbc driver operates at a low level within the USB subsystem, making it a potential entry point for malicious actors seeking to manipulate USB device communications or gain unauthorized access to system resources. The static nature of the buffer variable 'buf' means that even if the immediate buffer overflow is contained, the unpredictable data could still cause cascading failures throughout the kernel's memory management subsystem. This vulnerability directly relates to the ATT&CK technique T1068 which involves privilege escalation through kernel-level exploits.
The fix implemented for CVE-2023-53840 addresses the root cause by reserving an additional byte in the buffer allocation, ensuring that the buffer is automatically zeroed due to its static declaration. This simple yet effective mitigation prevents the out-of-bounds memory access by guaranteeing proper null termination of strings before they are processed by the trace function. The solution aligns with secure coding practices recommended by the CERT Secure Coding Standards, specifically addressing the need for proper buffer boundary checking and initialization. System administrators should prioritize applying this kernel patch immediately, as the vulnerability exists in the core USB handling mechanisms and could be exploited by malicious actors with physical access to affected systems or through USB-based attack vectors. The mitigation strategy effectively closes the memory access window while maintaining backward compatibility with existing USB device operations and debug tracing functionality.