CVE-2025-38604 in Linux
Summary
by MITRE • 08/19/2025
In the Linux kernel, the following vulnerability has been resolved:
wifi: rtl818x: Kill URBs before clearing tx status queue
In rtl8187_stop() move the call of usb_kill_anchored_urbs() before clearing b_tx_status.queue. This change prevents callbacks from using already freed skb due to anchor was not killed before freeing such skb.
BUG: kernel NULL pointer dereference, address: 0000000000000080 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 7 UID: 0 PID: 0 Comm: swapper/7 Not tainted 6.15.0 #8 PREEMPT(voluntary) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 RIP: 0010:ieee80211_tx_status_irqsafe+0x21/0xc0 [mac80211]
Call Trace: <IRQ> rtl8187_tx_cb+0x116/0x150 [rtl8187]
__usb_hcd_giveback_urb+0x9d/0x120 usb_giveback_urb_bh+0xbb/0x140 process_one_work+0x19b/0x3c0 bh_worker+0x1a7/0x210 tasklet_action+0x10/0x30 handle_softirqs+0xf0/0x340 __irq_exit_rcu+0xcd/0xf0 common_interrupt+0x85/0xa0 </IRQ>
Tested on RTL8187BvE device.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
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Analysis
by VulDB Data Team • 01/16/2026
The vulnerability CVE-2025-38604 affects the Linux kernel's wireless subsystem, specifically within the rtl8187 driver implementation for Realtek RTL8187BvE wireless devices. This issue represents a classic race condition and memory management flaw that can lead to kernel NULL pointer dereferences and system instability. The problem manifests during driver shutdown operations when the usb_kill_anchored_urbs() function is called after the tx status queue has already been cleared, creating a scenario where URB callbacks attempt to access already freed memory structures.
The technical root cause stems from improper ordering of operations within the rtl8187_stop() function where URB cleanup occurs after skb (socket buffer) deallocation. This sequence creates a window where asynchronous USB interrupt callbacks can execute and reference memory that has already been freed, resulting in a kernel NULL pointer dereference at address 0x80. The kernel oops trace shows the failure occurring in ieee80211_tx_status_irqsafe() function, which is part of the mac80211 subsystem responsible for IEEE 802.11 frame transmission status handling. The call stack demonstrates the typical path from USB HCD (Host Controller Driver) giveback operations through to the mac80211 transmission status processing, highlighting the chain of events that leads to the memory corruption.
This vulnerability has significant operational impact as it can cause system crashes and potential denial of service conditions in wireless networking environments. The issue affects systems running kernel versions including 6.15.0 and is particularly concerning for embedded systems or servers that rely on wireless connectivity. According to CWE classification, this vulnerability maps to CWE-415: Double Free and CWE-416: Use After Free, as the driver attempts to access memory that has been freed due to improper resource management ordering. The flaw also aligns with ATT&CK technique T1547.001: Registry Run Keys / Startup Folder, as the wireless subsystem could be exploited to maintain persistence or cause system instability during normal operation.
The mitigation strategy involves implementing proper resource cleanup ordering by ensuring usb_kill_anchored_urbs() is called before clearing the b_tx_status.queue. This change prevents asynchronous callbacks from accessing freed memory structures and eliminates the race condition that leads to the NULL pointer dereference. The fix demonstrates the importance of proper synchronization in kernel drivers, particularly when dealing with asynchronous operations and shared memory resources. System administrators should prioritize applying this kernel patch to all affected systems, especially those running wireless infrastructure or embedded devices that utilize the RTL8187 driver. The vulnerability was discovered through systematic kernel testing by the Linux Verification Center, highlighting the critical need for comprehensive testing of device drivers in kernel environments to identify such subtle but dangerous race conditions that can compromise system stability and security.