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CVE-2025-57808: Critical Vulnerability in ESPHome Web Server Authentication

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Overview

A critical vulnerability has been identified in the ESPHome system that has significant implications for microcontrollers used in Home Automation systems. This vulnerability, designated as CVE-2025-57808, allows unauthorized access to the web server functionalities, significantly increasing the risk of system compromise or data leakage. This flaw holds potential for severe damage as it permits access without any knowledge about the correct username or password. It is especially detrimental for systems with Over the Air (OTA) updates enabled, as the exploit could potentially introduce malicious firmware without detection.

Vulnerability Summary

CVE ID: CVE-2025-57808
Severity: Critical – CVSS Score 8.1
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Unauthorized access, potential system compromise, and data leakage

Affected Products

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Product | Affected Versions

ESPHome | 2025.8.0

How the Exploit Works

The vulnerability occurs in the ESPHome web_server’s authentication check, specifically when the client-supplied base64-encoded Authorization value is empty or is a substring of the correct value. This flaw allows the system to incorrectly pass the authentication check, providing unauthorized access to the web_server functionality. This means an attacker is able to access the web server, and if OTA is enabled, they are capable of manipulating the system by introducing potentially malicious firmware.

Conceptual Example Code

Here is a conceptual example illustrating how this vulnerability might be exploited. This HTTP request does not include a proper base64-encoded Authorization value, but due to the vulnerability, it is still accepted by the server:

GET /ota/update HTTP/1.1
Host: vulnerable-esphome.example.com
Authorization: Basic

In this example, the `Authorization: Basic ` header is empty, which should normally be rejected by the server. However, due to the CVE-2025-57808 vulnerability, this request would be accepted, allowing unauthorized access to the OTA update functionality.

Mitigation

The ESPHome team has patched this issue in version 2025.8.1. All users are strongly advised to update to this version or later to protect their systems. If an immediate update is not possible, use of a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can serve as temporary mitigation. However, these measures are not a permanent solution and the system update remains the most effective method to fully address this vulnerability.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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