ESPAsyncWebServer multipart parser has null-pointer write
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Fix
- Fixed in 3.11.2
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
ESPAsyncWebServer, an asynchronous HTTP and WebSocket server library used on ESP32, ESP8266, RP2040, and RP2350 microcontrollers, is affected when it handles multipart uploads such as file-upload or web-OTA endpoints. A specially crafted request can crash the device, causing it to reboot and resulting in a remote denial of service.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original 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.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- ESP32Async ESPAsyncWebServer
fixed in 3.11.2
References 3
GitHub · ESP32Async/ESPAsyncWebServer
Questions about CVE-2026-62966
What does this mean?
The multipart parser in ESPAsyncWebServer can write through a null pointer while handling a request body. A remote sender can crash the device, which then reboots and stops serving, a denial of service.Source: github.com
Am I affected, and how do I check?
Versions 3.11.1 and earlier of ESPAsyncWebServer are affected, and the bug is in src/WebRequest.cpp. It only matters if the device has a route with a non-trivial body or upload handler, such as a file-upload or web-OTA endpoint. To check, look at the library version in your project and whether any route uses a body or upload handler.Source: github.com
What should I do about it?
Upgrade ESPAsyncWebServer to 3.11.2 or later, which contains the fix.Source: github.com
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data