---
id: CVE-2026-54571
title: >-
  ESPAsyncWebServer is an asynchronous HTTP and WebSocket server library for
  ESP32, ESP8266, RP2040 and RP2350
summary: >-
  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
  _parseMu…
severity: high
cvss: 8.7
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'
cwe:
  - CWE-190
vendor: ESP32Async
product: ESPAsyncWebServer
affected:
  - ESPAsyncWebServer < 3.11.1
published: '2026-09-17'
updated: '2026-09-21'
sourceUpdated: '2026-09-21T21:17:04.560'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-54571'
references:
  - url: >-
      https://github.com/ESP32Async/ESPAsyncWebServer/commit/b928de7cbd7debcd6266ece6a6c46f10a86d3a6f
    label: security-advisories@github.com
  - url: 'https://github.com/ESP32Async/ESPAsyncWebServer/pull/445'
    label: security-advisories@github.com
  - url: 'https://github.com/ESP32Async/ESPAsyncWebServer/releases/tag/v3.11.1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/ESP32Async/ESPAsyncWebServer/security/advisories/GHSA-4phx-fcj6-46r4
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-21T21:05:35.710251Z'
cvssSource: cna
epss: 0.00301
epssPercentile: 0.22979
ingestedAt: '2026-09-17T19:26:25.318Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.