CVE-2026-64175 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: iwlwifi: mld: stop TX during firmware restart
When iwlwifi firmware crashes (e.g., NMI_INTERRUPT_UNKNOWN on Intel BE201/Wi-Fi 7), iwl_mld_nic_error() sets mld->fw_status.in_hw_restart to true. However, iwl_mld_tx_from_txq() does not check this flag before dequeuing frames from mac80211 and pushing them to the transport layer.
Since the firmware is dead, iwl_trans_tx() returns -EIO for each frame, which then gets freed immediately. Under high-throughput conditions (e.g., Tailscale UDP traffic or active SSH sessions), this creates a tight dequeue-send-fail-free loop that wastes CPU cycles and generates rapid skb allocation churn, leading to memory pressure from slab fragmentation.
The RX path already has this guard (iwl_mld_rx_mpdu checks in_hw_restart at rx.c:1906), and so does the TXQ allocation worker (iwl_mld_add_txqs_wk at tx.c:156). Add the same guard to iwl_mld_tx_from_txq() to stop all TX during firmware restart.
Frames left in mac80211's TXQs are naturally drained after restart completes, when queue reallocation triggers iwl_mld_tx_from_txq() via iwl_mld_add_txq_list(), or when new upper-layer traffic invokes wake_tx_queue.
Tested on ASUS Zenbook 14 UX3405CA with Intel BE201 (Wi-Fi 7) on kernel 6.19.5 where the firmware crashes approximately every 10-15 minutes under Tailscale traffic.
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Analysis
by VulDB Data Team • 07/20/2026
The vulnerability in question affects the iwlwifi driver within the Linux kernel, specifically targeting the mld (multi-link device) implementation used by Intel Wi-Fi 7 hardware. This issue manifests when the firmware experiences a crash scenario such as NMI_INTERRUPT_UNKNOWN on Intel BE201 devices, creating a critical operational failure in the wireless subsystem. The core problem lies in the improper handling of transmit operations during firmware restart procedures, where the driver fails to properly gate transmit activity despite recognizing that the firmware is no longer functional.
The technical flaw occurs within the iwl_mld_nic_error() function which correctly sets the mld->fw_status.in_hw_restart flag to true when a firmware crash is detected. However, the iwl_mld_tx_from_txq() function lacks proper validation of this critical flag before proceeding with frame dequeuing operations from mac80211's transmit queues. This oversight creates a dangerous race condition where frames are continuously dequeued, pushed to the transport layer, and immediately fail with -EIO error codes since the firmware is no longer capable of processing them. The continuous loop of dequeue-send-fail-free operations generates significant CPU overhead while simultaneously causing memory pressure through rapid skb allocation churn.
This vulnerability specifically impacts high-throughput network scenarios where sustained traffic patterns exacerbate the issue's severity. Under conditions such as Tailscale UDP traffic or active SSH sessions, the tight loop consumes substantial system resources and creates slab fragmentation that can lead to system instability. The RX path already implements proper protection through iwl_mld_rx_mpdu checks at line 1906 of rx.c, while the TXQ allocation worker includes similar safeguards in iwl_mld_add_txqs_wk at line 156 of tx.c. The missing guard in the TX path creates an asymmetric protection model that leaves transmit operations vulnerable during firmware restart states.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially destabilizing system resources under sustained load conditions. Memory pressure from slab fragmentation can manifest as reduced system responsiveness, increased latency, and in severe cases, system instability or crashes. The specific testing environment on ASUS Zenbook 14 UX3405CA with Intel BE201 hardware demonstrates that firmware crashes occur approximately every 10-15 minutes under Tailscale traffic conditions, indicating a systemic reliability issue that affects user experience and system availability.
The recommended mitigation involves implementing the same guard mechanism already present in other components of the driver by adding proper in_hw_restart flag checking to iwl_mld_tx_from_txq() function. This approach aligns with established security best practices for kernel module development where proper state management and defensive programming techniques are essential. The fix ensures that all transmit operations are halted during firmware restart periods, preventing the wasteful CPU cycles and memory pressure while allowing natural queue draining upon restart completion through existing mechanisms such as iwl_mld_add_txq_list() or new upper-layer traffic triggering wake_tx_queue operations.
This vulnerability type maps to CWE-691, which covers insufficient protection of code against excessive resource consumption, and aligns with ATT&CK techniques related to system resource exhaustion and denial of service conditions. The fix addresses the root cause by implementing proper state-based operation gating, similar to how other kernel subsystems handle similar scenarios during recovery operations. The solution maintains backward compatibility while preventing the specific race condition that leads to resource exhaustion and system instability under sustained network load conditions.