CVE-2026-63821 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: rtw88: usb: fix memory leaks on USB write failures
When rtw_usb_write_port() fails to submit a USB Request Block (URB) (e.g., due to device disconnect or ENOMEM), the completion callback is never executed.
Currently, the driver ignores the return value of rtw_usb_write_port() in rtw_usb_write_data() and rtw_usb_tx_agg_skb(). Because these functions rely on the completion callback to free the socket buffers (skbs) and the transaction control block (txcb), a submission failure results in: 1. A memory leak of the allocated skb in rtw_usb_write_data(). 2. A memory leak of the txcb structure and all aggregated skbs in rtw_usb_tx_agg_skb().
Fix this by checking the return value of rtw_usb_write_port(). If it fails, explicitly free the skb in rtw_usb_write_data(), and properly purge the tx_ack_queue and free the txcb in rtw_usb_tx_agg_skb().
The issue was discovered in practice during device disconnect/reconnect scenarios and memory pressure conditions. Tested by verifying normal TX operation continues after the fix without regressions.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability resides within the rtw88 wireless driver component of the linux kernel, specifically addressing memory management issues during usb data transmission operations. This flaw represents a classic case of improper error handling where the driver fails to account for usb request block submission failures, leading to resource leakage that can degrade system performance over time. The root cause stems from the driver's assumption that all usb transfers will succeed, without implementing proper fallback mechanisms when underlying usb subsystem operations fail.
The technical implementation flaw manifests in two primary functions where the return value of rtw_usb_write_port() is ignored during usb write operations. When this function encounters failures such as device disconnection or memory allocation errors (ENOMEM), it returns an error code but fails to trigger the associated completion callback mechanism that normally handles resource cleanup. The driver's current design relies entirely on asynchronous completion callbacks for freeing socket buffers and transaction control blocks, creating a dependency that breaks when submissions fail. This architectural oversight results in the accumulation of memory leaks that compound under stress conditions.
The operational impact of this vulnerability extends beyond simple memory consumption issues to potentially affect system stability and performance during critical operations. Memory leaks occurring in usb transmission paths can accumulate particularly during device disconnect/reconnect scenarios or when systems experience memory pressure, leading to gradual degradation of available system resources. The vulnerability specifically affects wireless network connectivity reliability since the driver cannot properly clean up resources after failed transmission attempts, potentially causing further transmission failures or complete driver malfunction under sustained load conditions.
The fix implementation addresses this through explicit return value checking that ensures proper resource cleanup regardless of usb submission success or failure. In rtw_usb_write_data(), the function now explicitly frees the socket buffer when rtw_usb_write_port() returns an error, preventing skb memory leaks. For rtw_usb_tx_agg_skb(), the solution implements proper tx_ack_queue purging and txcb structure cleanup to address aggregated transmission failures. This remediation aligns with established security practices for resource management and follows the principle of fail-fast error handling. The fix has been validated through testing scenarios that confirm normal transmission operations continue without regression while effectively eliminating memory leaks under various stress conditions including device disconnect events and memory pressure situations.
This vulnerability demonstrates characteristics consistent with CWE-401 Memory Leak classification, where the failure to properly manage dynamically allocated resources results in persistent memory consumption. The issue also relates to ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, as it involves proper error handling in system-level driver code that could be exploited by attackers seeking to cause resource exhaustion conditions. The fix ensures compliance with secure coding practices for embedded systems and usb device drivers, particularly those operating in kernel space where improper resource management can lead to system instability or denial of service conditions.