CVE-2026-63821 addresses a memory leak in the Linux kernel's rtw88 USB WiFi driver. When the function rtw_usb_write_port() fails to submit a USB Request Block (URB), the completion callback that normally frees allocated socket buffers (skbs) and transaction control blocks (txcb) is never called. The driver previously ignored the return value of this function in rtw_usb_write_data() and rtw_usb_tx_agg_skb(), resulting in memory leaks of skbs and txcb structures. The patch fixes this by checking the return value and explicitly freeing the allocated memory on failure, preventing leaks during device disconnect/reconnect and under memory pressure.

The vulnerability causes memory leaks in the Linux kernel's USB WiFi driver when USB write requests fail. This can lead to increased memory consumption and potential resource exhaustion on affected systems, especially during device disconnect/reconnect events or under memory pressure. There is no indication of code execution or privilege escalation from this issue.

A fix for this vulnerability has been implemented in the Linux kernel by correcting the driver to handle USB write failures properly and free allocated memory. Users should update to a Linux kernel version that includes this fix. Since no vendor advisory or patch links are provided, check the official Linux kernel repositories or distributions for the updated driver version containing this fix.