CVE-2023-53641 in Linux
Summary
by MITRE • 10/07/2025
In the Linux kernel, the following vulnerability has been resolved:
wifi: ath9k: hif_usb: fix memory leak of remain_skbs
hif_dev->remain_skb is allocated and used exclusively in ath9k_hif_usb_rx_stream(). It is implied that an allocated remain_skb is processed and subsequently freed (in error paths) only during the next call of ath9k_hif_usb_rx_stream().
So, if the urbs are deallocated between those two calls due to the device deinitialization or suspend, it is possible that ath9k_hif_usb_rx_stream() is not called next time and the allocated remain_skb is leaked. Our local Syzkaller instance was able to trigger that.
remain_skb makes sense when receiving two consecutive urbs which are logically linked together, i.e. a specific data field from the first skb indicates a cached skb to be allocated, memcpy'd with some data and subsequently processed in the next call to ath9k_hif_usb_rx_stream(). Urbs deallocation supposedly makes that link irrelevant so we need to free the cached skb in those cases.
Fix the leak by introducing a function to explicitly free remain_skb (if it is not NULL) when the rx urbs have been deallocated. remain_skb is NULL when it has not been allocated at all (hif_dev struct is kzalloced) or when it has been processed in next call to ath9k_hif_usb_rx_stream().
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 03/01/2026
The vulnerability CVE-2023-53641 represents a memory leak in the Linux kernel's ath9k wireless driver, specifically within the USB hardware interface layer. This issue affects the ath9k_hif_usb_rx_stream() function which handles USB receive operations for Atheros wireless network adapters. The flaw stems from improper memory management during the processing of USB transfer requests where allocated memory structures are not properly freed when device deinitialization or suspension occurs between consecutive USB operation cycles.
The technical implementation involves the hif_dev->remain_skb pointer which is allocated and utilized exclusively within the ath9k_hif_usb_rx_stream() function. This memory allocation occurs when processing two consecutive USB requests that are logically linked together, where the first request's data field indicates a cached skb (socket buffer) that needs to be allocated, copied with additional data, and then processed during the subsequent call to the same function. The design assumes that the remain_skb will be either processed and freed during the next function call or explicitly freed in error conditions.
However, the vulnerability emerges when USB transfer requests (URBs) are deallocated between the initial allocation and subsequent processing of remain_skb. During device deinitialization or system suspend operations, the URB deallocation process breaks the logical link between consecutive USB requests, rendering the cached skb irrelevant and causing the memory leak. The Syzkaller fuzzer, a sophisticated kernel testing tool, successfully triggered this condition by creating scenarios where device state changes occurred between USB processing cycles.
This memory leak vulnerability maps to CWE-401: "Improper Release of Memory Before Removing Last Reference" and represents a classic case of resource management failure in kernel space. The operational impact includes gradual memory consumption over time, potentially leading to system instability, performance degradation, or denial of service conditions when the leaked memory accumulates. The vulnerability affects systems running Linux kernels with the ath9k driver and USB-based wireless adapters, particularly those experiencing frequent device suspension or deinitialization events.
The fix implements a dedicated function to explicitly free the remain_skb memory when USB receive URBs have been deallocated, ensuring proper resource cleanup regardless of whether the next processing cycle occurs. This mitigation aligns with ATT&CK technique T1490: "Inhibit System Recovery" through proper memory management and prevents the accumulation of leaked memory that could eventually impact system stability and performance. The solution maintains the existing functionality while adding explicit cleanup logic that addresses the race condition between memory allocation and device state changes, ensuring that the hif_dev structure's remain_skb pointer is properly managed throughout the USB communication lifecycle.