CVE-2026-9263: Out-of-bounds read in Bluetooth Controller ISOAL framed RX reassembly leaks adjacent memory into host HCI ISO packets

The Zephyr Bluetooth controller ISO Adaptation Layer (subsys/bluetooth/controller/llsw/isoal.c) fails to validate the length field of a framed ISO PDU start segment. Per the Bluetooth specification a start segment (sc=0) always carries a 3-byte timeoffset, so its segment-header len must be at least PDUISOSEGTIMEOFFSETSIZE (3). isoalchecksegheader() accepted start segments with len < 3 as valid, and isoalrxframedconsume() then computed length = seghdr->len - 3 in a uint8t, underflowing to 253-255 when len is 0-2. That oversized length is passed to isoalrxappendtosdu(), whose copy is clamped only against the destination SDU buffer size, not the source PDU length, so up to ~255 bytes of controller memory beyond the received PDU are copied (via sinksduwritehci()/netbufaddmem) into an HCI ISO data packet and delivered to the host. The PDU and its segment headers are entirely attacker-controlled and arrive over the air, reachable through both the CIS and BIS-sync HCI data paths (hcidriver.c) and the vendor data path (ulliso.c), so a remote CIS peer or a broadcaster the device is synced to can trigger an out-of-bounds read causing information disclosure to the host and potential denial of service (faults or malformed oversized HCI ISO packets). The flaw affects all Zephyr releases since framed ISO reception was introduced in v3.0.0. The fix rejects sc=0 segments with len < 3 in isoalchecksegheader() and adds a guard before the subtraction in isoalrxframedconsume().