Contiki-NG is an open-source, cross-platform operating system for Next-Generation IoT devices. Versions prior to and including 4.8 are vulnerable to an out-of-bounds write that can occur in the BLE-L2CAP module. The Bluetooth Low Energy - Logical Link Control and Adaptation Layer Protocol (BLE-L2CAP) module handles fragmentation of packets up the configured MTU size. When fragments are reassembled, they are stored in a packet buffer of a configurable size, but there is no check to verify that the packet buffer is large enough to hold the reassembled packet. In Contiki-NG's default configuration, it is possible that an out-of-bounds write of up to 1152 bytes occurs. The vulnerability has been patched in the "develop" branch of Contiki-NG, and will be included in release 4.9. The problem can be fixed by applying the patch in Contiki-NG pull request #2254 prior to the release of version 4.9.