CVE-2026-54571 Details
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.
A denial-of-service vulnerability has been identified in the ESPAsyncWebServer library, which is used for asynchronous HTTP and WebSocket server functionality on ESP32, ESP8266, RP2040, and RP2350 platforms. The issue arises in the multipart/form-data parser, where the _boundaryPosition variable is stored as an 8-bit value. When a remote request includes a multipart boundary of exactly 256 bytes, this causes the boundary position to overflow, wrapping from 255 back to zero. This overflow prevents the boundary parsing loop from terminating, leading to excessive CPU usage and triggering a FreeRTOS watchdog reset on affected ESP32 or ESP8266 devices. The vulnerability exists in versions of ESPAsyncWebServer prior to 3.11.1.
Users can update to ESPAsyncWebServer version 3.11.1 or later, where this vulnerability has been fixed.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Sep 17, 2026CISA-ADP
Assessed Sep 21, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/ESP32Async/ESPAsyncWebServer/commit/b928de7cbd7debcd6266ece6a6c46f10a86d3a6f | [email protected] | Source CodeVendor |
| https://github.com/ESP32Async/ESPAsyncWebServer/pull/445 | [email protected] | Issue TrackingVendor |
| https://github.com/ESP32Async/ESPAsyncWebServer/releases/tag/v3.11.1 | [email protected] | Release NotesVendor |
| https://github.com/ESP32Async/ESPAsyncWebServer/security/advisories/GHSA-4phx-fcj6-46r4 | [email protected] | AdvisoryRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-190 | Integer Overflow or Wraparound | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| ESPAsyncWebServer | <= 3.11.0 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 21, 2026 | CVE Modified | CISA-ADP |
| Sep 17, 2026 | New CVE Received | [email protected] |