Informational 21 Bitcoin Committed Oct 16, 2025 · 09:25 UTC

u2f: Do not turn off BLE when U2F is used over USB

d6f22d77 View source ↗

Public commit record

What the developer wrote

Authored by Niklas Dusenlund

85/100 · Strong

u2f: Do not turn off BLE when U2F is used over USB

iOS devices support u2f over USB, so no need to disable BLE when only
u2f is used.

iOS devices also send one packet of garbage when waking up, 64 null
bytes, which also is ignored, so that the bitbox still can connect to
the iOS device when it is awakened.

✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Explains rationale or failure mode

The short version

What changed, and why it matters

This firmware update fixes a bug where using U2F security-key features over USB accidentally turned off Bluetooth Low Energy (BLE). Because iPhones and iPads can use U2F over USB, disabling BLE meant the device could not reconnect wirelessly after the iOS device woke up. The patch also makes the firmware ignore a harmless 64-byte 'wake-up' packet sent by iOS. There is no direct evidence this is an exploitable security vulnerability; it appears to be a connectivity/availability bug.

Recommended action

Treat as a functional/availability fix rather than a security patch. Reviewers may want to confirm that the inverted return value of usb_packet_process() does not affect other callers or state machines, and that ignoring the iOS wake-up frame cannot be abused to drop legitimate packets.

Security signals we found

Behavioral change in USB packet return values (true/false semantics inverted)

Removal of BLE power-down on U2F USB activity

Conditional BLE shutdown only after valid HWW packet processing

Explicit handling of 64-byte null 'garbage' wake-up packet from iOS

CHANGELOG labels it a bug fix, not a security fix

Technical analysis

Evidence from the diff

In the main loop, both HWW (main wallet) and U2F USB reads previously called communication_mode_ble_disable() unconditionally. The patch removes BLE shutdown from the U2F path and makes it conditional on usb_packet_process() returning true in the HWW path. usb_packet_process() return semantics are inverted: it now returns true on successful parse and false on ignored/invalid frames. This prevents an iOS wake-up garbage frame (64 null bytes) from shutting down BLE. The CHANGELOG frames the change as a bug fix for BLE being turned off when an iOS device is unlocked.

Changed components

src/firmware_main_loop.csrc/usb/usb_packet.csrc/usb/usb_packet.hBLE/U2F USB interaction subsystem

Inspect captured patch +17 / −21

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 85ed853..9eed3f5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ customers cannot upgrade their bootloader, its changes are recorded separately.
 ## Firmware
 
 ### [Unreleased]
+- Fix bug that BLE was turned off when iOS device is unlocked
 
 ### v9.24.0
 - Change title when entering recovery words to `1 of 24`, `2 of 24`, etc.
diff --git a/src/firmware_main_loop.c b/src/firmware_main_loop.c
index 8282b8d..e09bf3a 100644
--- a/src/firmware_main_loop.c
+++ b/src/firmware_main_loop.c
@@ -112,30 +112,25 @@ void firmware_main_loop(void)
 #endif
         // Do USB Input
         if (!hww_data && hid_hww_read(&hww_frame[0])) {
-            usb_packet_process((const USB_FRAME*)hww_frame);
-            if (communication_mode_ble_enabled()) {
-                // Enqueue a power down command to the da14531
-                da14531_power_down(&uart_write_queue);
-                // Flush out the power down command. This will be the last UART communication we do.
-                while (ringbuffer_num(&uart_write_queue) > 0) {
-                    uart_poll(NULL, 0, NULL, &uart_write_queue);
+            if (usb_packet_process((const USB_FRAME*)hww_frame)) {
+                if (communication_mode_ble_enabled()) {
+                    // Enqueue a power down command to the da14531
+                    da14531_power_down(&uart_write_queue);
+                    // Flush out the power down command. This will be the last UART communication we
+                    // do.
+                    while (ringbuffer_num(&uart_write_queue) > 0) {
+                        uart_poll(NULL, 0, NULL, &uart_write_queue);
+                    }
+                    communication_mode_ble_disable();
                 }
-                communication_mode_ble_disable();
+            } else {
+                util_log("usb_packet_process: invalid");
             }
         }
 #if APP_U2F == 1
         if (!u2f_data && hid_u2f_read(&u2f_frame[0])) {
             util_log("u2f data %s", util_dbg_hex((void*)u2f_frame, 16));
             u2f_packet_process((const USB_FRAME*)u2f_frame);
-            if (communication_mode_ble_enabled()) {
-                // Enqueue a power down command to the da14531
-                da14531_power_down(&uart_write_queue);
-                // Flush out the power down command. This will be the last UART communication we do.
-                while (ringbuffer_num(&uart_write_queue) > 0) {
-                    uart_poll(NULL, 0, NULL, &uart_write_queue);
-                }
-                communication_mode_ble_disable();
-            }
         }
 #endif
 
@@ -156,7 +151,7 @@ void firmware_main_loop(void)
             }
         }
 #if APP_U2F == 1
-        if (!communication_mode_ble_enabled() && u2f_data) {
+        if (u2f_data) {
             if (hid_u2f_write_poll(u2f_data)) {
                 util_log("u2f wrote %s", util_dbg_hex(u2f_data, 16));
                 u2f_data = NULL;
diff --git a/src/usb/usb_packet.c b/src/usb/usb_packet.c
index b22620b..991a1cf 100644
--- a/src/usb/usb_packet.c
+++ b/src/usb/usb_packet.c
@@ -67,7 +67,7 @@ bool usb_packet_process(const USB_FRAME* frame)
     switch (usb_frame_process(frame, &_in_state)) {
     case FRAME_ERR_IGNORE:
         // Ignore this frame, i.e. no response.
-        break;
+        return false;
     case FRAME_ERR_INVALID_SEQ:
         // Reset the state becuase this error indicates that there is a host application bug
         _reset_state();
@@ -92,7 +92,7 @@ bool usb_packet_process(const USB_FRAME* frame)
                 ctx, _in_state.data, _in_state.len, _in_state.cmd, _in_state.cid)) {
             // Queue filled and will be sent during usb processing
             _reset_state();
-            return false;
+            return true;
         }
         // Else: Currently processing a message, reset the state and forget about this packet
         _reset_state();
diff --git a/src/usb/usb_packet.h b/src/usb/usb_packet.h
index a037f69..f289c8e 100644
--- a/src/usb/usb_packet.h
+++ b/src/usb/usb_packet.h
@@ -42,7 +42,7 @@ typedef struct {
 /**
  * Processes an incoming USB packet.
  * @param[in] frame The frame that is to be processed.
- * @return true if we are waiting for more frames to complete a packet, false otherwise.
+ * @return true if packet was successfully parsed, false otherwise
  */
 bool usb_packet_process(const USB_FRAME* frame);

Risk score

Why this scored 21/100

Our methodology →

Potential impact 3/30

Exploitability 2/25

Stealth signal 2/15

Affected reach 4/15

Confidence 7/10

Evidence quality 3/5

Human-validated context

Community notes

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What the developer wrote

What changed, and why it matters

Security signals we found

Evidence from the diff

Changed components

Why this scored 21/100

Community notes

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