Vulnerability Description
ESPAsyncWebServer is an asynchronous HTTP and WebSocket server library for ESP32, ESP8266, RP2040 and RP2350. Prior to version 3.11.2, the multipart parser in `src/WebRequest.cpp` frees `_itemBuffer` and sets it to NULL when `BOUNDARY_OR_DATA` matches the closing boundary of a file part, before confirming the following terminator, while leaving `_itemIsFile` true. If the next byte is neither the final closing dashes nor a clean CRLF, the `DASH3_OR_RETURN2` or `EXPECT_FEED2` rewind branch re-injects provisionally consumed bytes through `itemWriteByte`. Because `_itemIsFile` remains true, `_itemBuffer`[`_itemBufferIndex`++] writes through a null pointer. On ESP32 this causes a `StoreProhibited` exception, panic and device reboot, producing remote denial of service. A route with a non-trivial body/upload handler, such as a file-upload or web-OTA endpoint, must be present. This issue is fixed in version 3.11.2.
CVSS Score
HIGH
Related Weaknesses (CWE)
References
- https://github.com/ESP32Async/ESPAsyncWebServer/commit/4efbd35e597d91f01749f2d4a
- https://github.com/ESP32Async/ESPAsyncWebServer/security/advisories/GHSA-8m8p-vh
- https://github.com/ESP32Async/ESPAsyncWebServer/tree/v3.11.2
FAQ
What is CVE-2026-62966?
CVE-2026-62966 is a vulnerability with a CVSS score of 7.5 (HIGH). ESPAsyncWebServer is an asynchronous HTTP and WebSocket server library for ESP32, ESP8266, RP2040 and RP2350. Prior to version 3.11.2, the multipart parser in `src/WebRequest.cpp` frees `_itemBuffer` ...
How severe is CVE-2026-62966?
CVE-2026-62966 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-62966?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.