CVE-2026-54571 – ESPAsyncWebServer: Integer overflow in multipart boundary parser causes denial of service

​CVE ID :CVE-2026-54571

Published : Sept. 17, 2026, 7:16 p.m. | 1 hour, 3 minutes ago

Description :ESPAsyncWebServer is an asynchronous HTTP and WebSocket server library for ESP32, ESP8266, RP2040 and RP2350. Prior to 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. This issue is fixed in version 3.11.1.

Severity: 8.7 | HIGH

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