CVE-2025-59513 - Out-of-Bounds Read in Windows Bluetooth RFCOM Protocol Driver – Detailed Analysis and Exploit Walkthrough

Microsoft’s Bluetooth RFCOMM protocol driver has recently come under the security spotlight, with the disclosure of a significant vulnerability tracked as CVE-2025-59513. This bug exposes sensitive system information on Windows devices to local, authorized attackers. In this article, we’ll break down the vulnerability, examine how an attacker can exploit it, and provide code snippets demonstrating an information leak. If you’re a Windows user or a security researcher, this is a read you won’t want to skip.

What is CVE-2025-59513?

CVE-2025-59513 is an out-of-bounds read vulnerability in the Windows Bluetooth RFCOMM (Radio Frequency Communication) protocol driver. RFCOMM is crucial for serial communication over the Bluetooth stack, essentially emulating serial ports across Bluetooth.

In Simple Terms

- The flaw allows a user with local access to exploit the RFCOMM driver, tricking it into reading memory it shouldn’t.

This memory can contain secrets, kernel pointers, or other information useful to attackers.

- The attacker needs to have valid credentials on the system—this is *not* remotely exploitable or wormable.

The attacker opens a Bluetooth connection and interacts with the RFCOMM driver at a low level.

Send Crafted Packets:

By sending specially crafted API calls or data packets to the driver, the attacker manipulates the length fields or data structures.

Trigger Out-of-Bounds Read:

The driver then inadvertently reads more memory than it should and returns unauthorized data to the attacker.

Vulnerable Code Path (Pseudocode)

While the original driver code is closed source, Microsoft’s description gives us clues. Here’s a simplified example (not the real source, but enough to understand):

// Hypothetical pseudocode illustrating the issue

void handle_rfcomm_message(const uint8_t* data, size_t len) {
    uint8_t header_size = data[];
    uint8_t content[128];

    // Fails to properly check header_size and len
    memcpy(content, data + 1, header_size); // Potential out-of-bounds read!
    // ... further processing
}

If header_size is larger than the actual message, it reads past what the user sent—spilling over into kernel memory.

Proof-of-Concept (PoC) – Information Disclosure

Below is a Windows userland PoC (conceptual, for educational use only!) using the Windows Bluetooth API to transmit a malformed packet to the RFCOMM driver. This relies on the attacker already having access to the machine.

import ctypes
from ctypes import wintypes

# Use PyBluez or directly Windows APIs (pseudo)

def send_rfcomm_malformed():
    # Open Bluetooth RFCOMM channel (normally with PyBluez/Windows API)
    # Assume already paired and connected

    # Craft a malformed RFCOMM data packet
    malformed_data = b'\xFF' + b'A'*10  # header_size way beyond what we send

    # Send to vulnerable driver endpoint (abstract)
    with open_rfcomm_channel() as channel:
        channel.send(malformed_data)
        leaked_data = channel.recv(200)
        print("Leaked Memory Data:", leaked_data)

# Function stubs for context
def open_rfcomm_channel():
    # Here you'd interact with PyBluez or Windows Bluetooth API
    raise NotImplementedError("Stub for opening RFCOMM channel.")

send_rfcomm_malformed()

This PoC would result in extra data being read back from driver memory, possibly including sensitive or kernel-space contents.

Original References

- Microsoft Security Advisory (June 2025 Patch Tuesday)
- MITRE CVE Database Entry
- Bluetooth Core Spec (Bluetooth SIG)

What Can Attackers Gain?

- Information Disclosure: Kernel pointers, private data used by processes, or cryptographic secrets.
- Potential for Privilege Escalation (with chaining): While *this* bug doesn’t grant code execution, it can be used with other bugs to break out of sandboxes or ASLR defenses.

Conclusion

CVE-2025-59513 highlights the ongoing challenge of memory safety in complex protocol drivers, even in modern operating systems like Windows. If you’re a system administrator, apply the patch without delay. If you’re a security researcher, this is a great case study on the importance of bounds checking and least privilege principles.

Stay safe and keep your systems updated!

*This post is original content, intended for educational purposes. For more details, refer to the Microsoft Security Portal.*

Timeline

Published on: 11/11/2025 18:15:37 UTC
Last modified on: 12/09/2025 22:38:47 UTC