The nRF link-layer receive paths of the open-source Bluetooth LE Controller did not validate the on-air LENGTH field of a received PDU against the maximum receive length that was used to program the radio. isr_rx_pdu() in subsys/bluetooth/controller/ll_sw/nordic/lll/lll_conn.c enqueued any non-empty data PDU after only the sequence-number and (for encrypted links) MIC checks, and the corresponding isr_rx() handlers in lll_central_iso.c, lll_peripheral_iso.c, lll_sync_iso.c and lll_scan_aux.c did the same for ISO and extended-advertising PDUs. The nRF radio stores the received header verbatim and truncates only the payload at PCNF1.MAXLEN, so a frame declaring more octets than were configured leaves a node buffer whose len field describes more data than the buffer holds.

An attacker within radio range that can emit a hand-crafted link-layer PDU — for a connection, any peer that establishes an unencrypted LE connection to a connectable advertiser; for CONFIG_BT_CTLR_SYNC_ISO, any broadcaster the device is synchronised to — can set the length byte up to 255 while the controller has programmed a much smaller maximum (lll->dle.eff.max_rx_octets, which is 27 until a Data Length Update, or the negotiated cis_lll->rx.max_pdu). No pairing, authentication or user interaction is required. On encrypted links the CCM MIC check normally rejects such a frame first, so the exposure is on unencrypted traffic, which is why the added check is placed after decryption.

The unchecked length rea…