RIOT-OS, an operating system for Internet of Things (IoT) devices, contains a network stack with the ability to process 6LoWPAN frames. In versions 2023.01 and prior, an attacker can send a crafted frame which is forwarded by the device. During encoding of the packet a NULL pointer dereference occurs. This crashes the device leading to denial of service. A patch is available at pull request 19678. There are no known workarounds.