CVE-2026-54571

42th percentile - higher than 42% of all known CVEs

In ESPAsyncWebServer (an asynchronous HTTP and WebSocket server library for ESP32, ESP8266, RP2040 and RP2350) before version 3.11.1, the multipart/form-data parser in src/WebRequest.cpp stores _boundaryPosition as an 8-bit value while _parseMultipartPostByte processes the boundary. A remote request containing an exactly 256-byte multipart boundary wraps _boundaryPosition from 255 to zero, prevents the boundary parsing loop from terminating, consumes excessive CPU, and triggers a FreeRTOS watchdog reset on affected ESP32 or ESP8266 devices. The issue is fixed in version 3.11.1.

A remote attacker can cause the parsing loop to hang, consume excessive CPU, and trigger a watchdog reset with a single request, restarting the device and disrupting service. This affects ESP32 and ESP8266 devices.

Update the ESPAsyncWebServer library to version 3.11.1 or later. Until then, consider restricting access to devices and monitoring for unexpected reboots.