CVE-2025-53540: Arduino-ESP32 CSRF Vulnerability

CVE-2025-53540 Overview

CVE-2025-53540 is a Cross-Site Request Forgery (CSRF) vulnerability [CWE-352] affecting the arduino-esp32 framework. The arduino-esp32 project provides Arduino core support for ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6, and ESP32-H2 microcontrollers. Several Over-the-Air (OTA) update examples and the HTTPUpdateServer implementation accept firmware upload POST requests without CSRF protection. An attacker can trick an authenticated user into submitting a malicious firmware upload, achieving remote code execution on the target microcontroller. The vulnerability is fixed in version 3.2.1.

Critical Impact

Successful exploitation allows attackers to upload and execute arbitrary firmware on affected ESP32 devices, resulting in full remote code execution and persistent device compromise.

Affected Products

• arduino-esp32 versions prior to 3.2.1
• HTTPUpdateServer implementation in arduino-esp32
• OTA update example sketches shipped with arduino-esp32

Discovery Timeline

• 2025-07-07 - CVE-2025-53540 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-53540

Vulnerability Analysis

The vulnerability resides in the OTA firmware update workflow exposed by arduino-esp32. The HTTPUpdateServer implementation and several reference OTA examples expose HTTP POST endpoints that accept firmware binaries for upload and flashing. These endpoints lack anti-CSRF tokens, origin validation, or any state-changing request protections.

Because the endpoints process multipart POST requests directly from any source that can reach the device, an attacker-controlled web page can issue a cross-origin form submission that delivers malicious firmware. If a user with network access to the device visits the attacker's page while authenticated, the browser submits the firmware payload using the user's session context.

The device accepts the upload, writes it to flash, and reboots into the attacker-supplied firmware. This grants the attacker arbitrary code execution on the microcontroller with full hardware access.

Root Cause

The root cause is missing CSRF protection on state-changing HTTP endpoints. The OTA update handlers do not validate request origin, do not require anti-CSRF tokens, and do not enforce same-origin policies before accepting firmware uploads. Basic authentication, where used, only proves the user's identity to the device but does not prove that the user intentionally initiated the upload request.

Attack Vector

An attacker hosts a malicious web page containing a hidden HTML form that targets the OTA update endpoint of a known ESP32 device on the victim's network. When the victim visits the page, the browser automatically submits the form along with cached credentials. The firmware payload is processed and flashed by the device. The attack requires user interaction to visit the malicious page but no direct interaction with the target device.

The vulnerability is described in detail in the GitHub Security Advisory GHSA-9vfw-wx65-c872.

Detection Methods for CVE-2025-53540

Indicators of Compromise

• Unexpected POST requests to OTA endpoints such as /update, /firmware, or example handler paths on ESP32 devices
• HTTP requests to OTA endpoints carrying a Referer or Origin header that does not match the device's management interface
• Unscheduled firmware version changes or device reboots immediately following inbound HTTP POST traffic
• Outbound connections from ESP32 devices to unfamiliar command-and-control endpoints after a suspected update event

Detection Strategies

• Inspect web server and proxy logs for multipart Content-Type: multipart/form-data POST requests directed at ESP32 device IP addresses
• Audit deployed firmware build hashes against a known-good baseline to identify unauthorized images
• Monitor for cross-origin POST submissions targeting embedded device subnets from user workstations

Monitoring Recommendations

• Aggregate HTTP traffic logs from networks hosting ESP32 fleets and alert on POST traffic to update endpoints
• Enable device-side logging of firmware update attempts including source IP, timestamp, and request headers
• Track NVD and the arduino-esp32 GitHub repository for updated guidance and downstream advisories

How to Mitigate CVE-2025-53540

Immediate Actions Required

• Upgrade arduino-esp32 to version 3.2.1 or later and rebuild and re-flash all affected devices
• Remove or disable the vulnerable HTTPUpdateServer and example OTA handlers from production firmware until patched
• Restrict network access to OTA endpoints using firewall rules, VLAN segmentation, or VPN-only management access
• Rotate any credentials used to authenticate to the OTA interface after patching

Patch Information

The fix is delivered in arduino-esp32 release 3.2.1. The corrective change is available in the upstream commit f4fdecc, which introduces CSRF protections to the OTA update flow. Developers must rebuild dependent sketches and libraries against the patched core and deploy new firmware to all devices, as the vulnerability cannot be remediated through configuration alone.

Workarounds

• Place ESP32 devices on isolated management networks unreachable from user browsing environments
• Disable the HTTP-based OTA update interface and use a signed, pull-based update mechanism initiated by the device
• Implement a reverse proxy in front of the device that enforces origin checks and rejects cross-origin POST requests
• Require explicit, out-of-band confirmation before firmware uploads are accepted on the device

# Example: restrict OTA endpoint access with iptables on a gateway
iptables -A FORWARD -p tcp -d <esp32_ip> --dport 80 -m state --state NEW -j DROP
iptables -A FORWARD -p tcp -s <management_workstation_ip> -d <esp32_ip> --dport 80 -j ACCEPT