● CVE-2024-0044 / Zero-Click Bluetooth

CVE-2024-0044: Android Fluoride Bluetooth HCI Heap Buffer Overflow Teardown

How an unchecked fragmentation boundary mismatch in system/bt/stack/l2cap enabled zero-click remote code execution over Bluetooth.

💡 आसान भाषा में समझें (ELI5)

Imagine a post office that accepts letters in numbered pieces (Part 1 of 2, Part 2 of 2). An attacker sends Part 1 stating 'the whole letter is 50 words'. The clerk prepares a tiny envelope. Then the attacker sends Part 2 containing 5,000 words! The clerk shoves the words in, bursting the envelope and scattering private documents all over the floor.

महत्वपूर्ण तकनीकी अवधारणाएं और शब्द

Fluoride Bluetooth Stack
The open-source C/C++ Bluetooth protocol stack used in Android, handling L2CAP, SDP, and RFCOMM.
HCI (Host Controller Interface)
The protocol layer communicating between the software Bluetooth stack and the hardware radio chip.
L2CAP (Logical Link Control and Adaptation Protocol)
The protocol responsible for segmenting and reassembling network packets across Bluetooth links.
Heap Buffer Overflow
Writing packet payload data past the allocated boundaries of a heap chunk.

कदम-दर-कदम हमले की तकनीकी प्रक्रिया

Step 1

1. Attacker in Bluetooth Range

The attacker broadcasts crafted ACL packets toward a nearby Android device.

Step 2

2. Sending Incomplete First Fragment

The attacker sends an initial L2CAP packet claiming a small total packet length.

Step 3

3. Sending Oversized Continuation Packet

The attacker sends a second fragment with an unexpected payload size exceeding the allocation.

Step 4

4. Heap Corruption in com.android.bluetooth

The reassembly loop overwrites adjacent heap chunks, executing code inside the Bluetooth daemon.

सोर्स कोड तुलना: असुरक्षित कोड बनाम सुरक्षित सुधार

सरल और समझने योग्य उच्च स्तरीय प्रोग्रामिंग कोड में प्रस्तुत (बिना किसी बाइनरी या असेंबली के)।

असुरक्षित कोड (त्रुटिपूर्ण)
// VULNERABLE: system/bt/stack/l2cap/l2c_main.cc
void l2c_rcv_acl_data(BT_HDR *p_msg) {
    tL2C_LCB *p_lcb = l2cu_find_lcb_by_handle(handle);
    
    // ROOT CAUSE:
    // Does not verify that accumulated fragment lengths stay within allocated buffer!
    uint8_t *p_dest = p_lcb->p_rx_msg->data + p_lcb->p_rx_msg->offset;
    
    // Copies fragment without boundary checking!
    memcpy(p_dest, p_msg->data, p_msg->len);
    p_lcb->p_rx_msg->offset += p_msg->len;
}
सुरक्षित पैच (सुधार)
// SECURE: system/bt/stack/l2cap/l2c_main.cc patch
void l2c_rcv_acl_data(BT_HDR *p_msg) {
    tL2C_LCB *p_lcb = l2cu_find_lcb_by_handle(handle);
    
    // 1. Calculate remaining capacity in allocated reassembly buffer
    size_t remaining_capacity = p_lcb->p_rx_msg->total_len - p_lcb->p_rx_msg->offset;
    
    // 2. Reject fragment if incoming length exceeds remaining capacity
    if (p_msg->len > remaining_capacity) {
        L2CAP_TRACE_ERROR("L2CAP packet overflow: len %d exceeds remaining %zu", 
                          p_msg->len, remaining_capacity);
        osi_free(p_lcb->p_rx_msg);
        p_lcb->p_rx_msg = nullptr;
        return; // Abort cleanly
    }
    
    uint8_t *p_dest = p_lcb->p_rx_msg->data + p_lcb->p_rx_msg->offset;
    memcpy(p_dest, p_msg->data, p_msg->len);
    p_lcb->p_rx_msg->offset += p_msg->len;
}

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