CVE-2026-25508: ESP-IDF Buffer Overflow Vulnerability

CVE-2026-25508 Overview

CVE-2026-25508 is an out-of-bounds read vulnerability affecting the Espressif ESP-IDF (Internet of Things Development Framework). The vulnerability exists in the BLE ATT Prepare Write handling within the BLE provisioning transport component (protocomm_ble). A remote attacker within BLE range can exploit this flaw while a target device is in provisioning mode to trigger an out-of-bounds read, potentially leading to memory corruption and denial of service.

The vulnerability stems from improper tracking of cumulative buffer length when handling prepared-write fragments. By sending repeated prepare write requests with overlapping offsets, an attacker can cause the reported length to exceed the allocated buffer size, which is then passed to provisioning handlers during execute-write processing.

Critical Impact

Remote attackers within adjacent network (BLE) range can exploit vulnerable ESP32 devices during provisioning to cause memory corruption and denial of service without authentication.

Affected Products

• ESP-IDF version 5.5.2
• ESP-IDF version 5.4.3
• ESP-IDF version 5.3.4
• ESP-IDF version 5.2.6
• ESP-IDF version 5.1.6

Discovery Timeline

• 2026-02-04 - CVE-2026-25508 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-25508

Vulnerability Analysis

This out-of-bounds read vulnerability (CWE-125) affects the BLE provisioning transport layer in ESP-IDF. The protocomm_ble component is responsible for handling BLE-based provisioning communications, which allows users to configure Wi-Fi credentials and other settings on ESP32 devices via Bluetooth Low Energy.

The core issue lies in how the transport accumulates prepared-write fragments during BLE ATT (Attribute Protocol) operations. The BLE specification allows clients to send prepared write requests to queue up data before an execute write command commits the data. The vulnerable implementation uses a fixed-size buffer to store these fragments but fails to correctly track the cumulative length of received data.

When a malicious BLE client sends repeated prepare write requests with overlapping offsets, the length tracking mechanism becomes corrupted. The reported length value can exceed the actual allocated buffer size. This inflated length is subsequently passed to provisioning handlers during execute-write processing, resulting in an out-of-bounds read operation where the handler attempts to process more data than the buffer actually contains.

The attack requires the device to be in provisioning mode and the attacker to be within BLE range (adjacent network), limiting the attack surface but still presenting a significant risk for IoT deployments where provisioning may occur in public or shared spaces.

Root Cause

The root cause is improper bounds checking and length validation in the BLE ATT prepared write handling code. The protocomm_ble component incorrectly tracks cumulative fragment lengths when processing overlapping offset values in prepare write requests. This allows the internal length counter to exceed the actual allocated buffer size, creating a mismatch between the tracked length and the buffer's true capacity.

Attack Vector

The attack requires adjacent network access via Bluetooth Low Energy. An attacker must:

1. Be within BLE range of a vulnerable ESP32 device
2. Wait for or trigger the device to enter provisioning mode
3. Establish a BLE connection to the device's provisioning service
4. Send crafted prepare write requests with overlapping offsets to inflate the tracked buffer length
5. Issue an execute write command to trigger the out-of-bounds read during provisioning handler processing

The attack does not require authentication but does require user interaction (the device must be placed in provisioning mode). The vulnerability can result in information disclosure through memory reads beyond buffer boundaries and high availability impact through potential crashes or memory corruption.

The exploitation mechanism involves manipulating the BLE ATT Prepare Write operation, which is part of the standard Bluetooth Low Energy attribute protocol. By sending multiple prepare write requests targeting the same or overlapping buffer offsets, the attacker can cause the ESP-IDF implementation to miscalculate the total data length, ultimately triggering an out-of-bounds memory access. For complete technical details, refer to the GitHub Security Advisory.

Detection Methods for CVE-2026-25508

Indicators of Compromise

• Unexpected device crashes or reboots during BLE provisioning operations
• Anomalous BLE connection patterns with multiple prepare write requests from the same client
• Memory corruption indicators such as stack canary violations or heap corruption messages in device logs
• Unusual BLE ATT protocol sequences with overlapping offset values in prepare write operations

Detection Strategies

• Monitor ESP32 device logs for memory-related errors during provisioning mode, particularly heap corruption or buffer overflow warnings
• Implement BLE traffic analysis to detect anomalous prepare write patterns with overlapping offsets
• Use firmware integrity monitoring to detect unexpected behavior changes in provisioning components
• Deploy network-level BLE monitoring in sensitive deployment environments to identify suspicious connection attempts

Monitoring Recommendations

• Enable verbose logging for the protocomm_ble component during development and testing phases
• Implement device health monitoring that tracks provisioning session anomalies and unexpected terminations
• Configure alerts for devices that experience repeated crashes during provisioning operations
• Maintain an inventory of ESP-IDF versions in use across deployments to quickly identify vulnerable devices

How to Mitigate CVE-2026-25508

Immediate Actions Required

• Update all affected ESP-IDF installations to patched versions: 5.5.3, 5.4.4, 5.3.5, 5.2.7, or 5.1.7
• Minimize the time devices spend in provisioning mode and avoid provisioning in public or untrusted environments
• Consider disabling BLE provisioning if not required for your use case and use alternative provisioning methods
• Audit deployed devices to identify those running vulnerable ESP-IDF versions

Patch Information

Espressif has released security patches addressing this vulnerability in ESP-IDF versions 5.5.3, 5.4.4, 5.3.5, 5.2.7, and 5.1.7. The fixes correct the length tracking logic in the BLE ATT prepared write handling to properly validate cumulative buffer lengths.

Multiple commits have been published to address this issue:

• Espressif Commit Fix
• Espressif Commit Update
• Espressif Commit Improvement

For complete details, see the GitHub Security Advisory.

Workarounds

• Disable BLE provisioning entirely if alternative provisioning methods (SoftAP, serial) are acceptable for your deployment
• Implement physical access controls to limit who can be in BLE range during device provisioning
• Reduce BLE advertising power or range during provisioning to minimize the attack surface
• Implement application-level timeouts that exit provisioning mode after a short period of inactivity

# ESP-IDF version upgrade commands
cd ~/esp/esp-idf
git fetch --all --tags
git checkout v5.5.3  # or appropriate patched version for your branch
git submodule update --init --recursive
./install.sh
source export.sh