CVE-2026-54571 ESPAsyncWebServer: Integer overflow in multipart boundary parser causes denial of service
Remote attackers can cause denial of service on ESP32/ESP8266 devices by sending a 256-byte multipart boundary, triggering an infinite loop and watchdog reset.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-54571?
CVE-2026-54571 is a high-severity vulnerability in ESP32Async ESPAsyncWebServer, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-190
Which versions are affected by CVE-2026-54571?
How do I fix CVE-2026-54571?
No fix has been published for CVE-2026-54571 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-54571 being exploited?
There is no known exploitation of CVE-2026-54571 in the wild and no public exploit code.
Sources
Also known as GHSA-4phx-fcj6-46r4.