Heap Out-of-Bounds Write in Tasmota IoT Firmware

Executive Summary

This is a heap out-of-bounds write vulnerability in Tasmota versions up to 16.0.0. It occurs in the SendReceiveDeviceGroupMessage() function when processing crafted Device Groups messages over UDP port 4447. The flaw allows unauthenticated local network attackers to corrupt heap memory by making the log_remaining counter negative, causing writes to exceed a fixed 512-byte buffer. This can crash devices or potentially enable native code execution on ESP8266 and ESP32 platforms which lack ASLR and heap cookies.

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Detection Guidance

To detect this vulnerability, monitor UDP traffic on port 4447 for malformed Device Groups messages. Use Wireshark or tcpdump to capture packets and inspect for messages exceeding 512 bytes or containing negative log_remaining values. Check Tasmota device logs for crashes or memory corruption errors.

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Impact Analysis

If you use Tasmota devices on your local network, attackers could exploit this to crash your devices or execute malicious code on them. This could disrupt IoT operations, allow unauthorized access to device functions, or potentially compromise connected systems. The impact is higher for ESP8266/ESP32 devices due to their lack of memory protection features.

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Mitigation Strategies

Immediately update Tasmota to a version containing commit e97e1e4 or later. Block UDP port 4447 at the network perimeter if Device Groups functionality is not required. Monitor devices for unusual behavior and apply patches as soon as possible.

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