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CVE-2026-23833: CVE-2026-23833: The 4GB Loophole in Your Light Switch

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CVE-2026-23833: The 4GB Loophole in Your Light Switch

Vulnerability ID: CVE-2026-23833
CVSS Score: 7.5
Published: 2026-01-21

A classic integer overflow in ESPHome's API protobuf decoder allows remote attackers to crash devices by sending a malformed packet. This vulnerability highlights the dangers of pointer arithmetic in C++ on 32-bit microcontrollers.

TL;DR

ESPHome, the software running on millions of DIY smart home devices, has a remote denial-of-service vulnerability. By sending a specially crafted protobuf message with a massive length field, an attacker can trigger an integer overflow during a safety check. This bypasses the buffer protection, causes the device to read invalid memory, and forces a hard crash/reboot. If you aren't using API encryption, anyone on your Wi-Fi can flicker your lights off indefinitely.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-190
  • Attack Vector: Network (TCP/6053)
  • CVSS v4.0: 1.7 (Official)
  • Real World Severity: Medium/High (DoS)
  • Impact: Device Crash / Boot Loop
  • Exploit Status: PoC Available

Affected Systems

  • ESPHome Framework (2025.9.0 - 2025.12.6)
  • ESP32
  • ESP8266
  • RP2040
  • LibreTiny
  • ESPHome: 2025.9.0 - 2025.12.6 (Fixed in: 2025.12.7)

Code Analysis

Commit: 69d7b6e

Fix integer overflow in proto decoder

- if (ptr + field_length > end) {
+ if (field_length > static_cast<size_t>(end - ptr)) {
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Exploit Details

  • Internal Research: Theoretical PoC based on patch analysis involves sending Protobuf WireType 2 with length 0xFFFFFFFF.

Mitigation Strategies

  • Update Firmware
  • Enable API Encryption
  • Network Segmentation (VLANs)

Remediation Steps:

  1. Identify all devices running ESPHome versions 2025.9.0 through 2025.12.6.
  2. Update the ESPHome dashboard to version 2025.12.7 or newer.
  3. Recompile firmware for all nodes.
  4. Perform Over-the-Air (OTA) updates for all nodes.
  5. Verify that the 'api' component in your YAML includes an 'encryption' key.

References

Read the full report for CVE-2026-23833 on our website for more details including interactive diagrams and full exploit analysis.

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