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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

No CVSS v3.1

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
ESP32Async ESPAsyncWebServer affected
Version Status Constraints
< 3.11.1 affected —

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Project Subscriptions

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Advisories

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Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/ESP32Async/ESPAsyncWebServer/commit/b928de7cbd7debcd6266ece6a6c46f10a86d3a6f cve-icon
https://github.com/ESP32Async/ESPAsyncWebServer/pull/445 cve-icon
https://github.com/ESP32Async/ESPAsyncWebServer/releases/tag/v3.11.1 cve-icon
https://github.com/ESP32Async/ESPAsyncWebServer/security/advisories/GHSA-4phx-fcj6-46r4 cve-icon
History

Thu, 17 Sep 2026 18:45:00 +0000

Type Values Removed Values Added
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.
Title ESPAsyncWebServer: Integer overflow in multipart boundary parser causes denial of service
Weaknesses CWE-190
References
Metrics cvssV4_0

{'score': 8.7, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-17T18:28:26.977Z

Reserved: 2026-06-15T19:15:27.343Z

Link: CVE-2026-54571

cve-icon Vulnrichment

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cve-icon NVD

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cve-icon Redhat

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cve-icon OpenCVE Enrichment

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Weaknesses