{"id":"CVE-2026-12363","summary":"Out-of-bounds write in LoRaWAN fragmented transport from a fragment index of 0","details":"The LoRaWAN Fragmented Data Block Transport service (subsys/lorawan/services/frag_transport.c) does not validate the fragment counter in a received DATA_FRAGMENT command before forwarding it to the configured decoder. In frag_transport_package_callback() the value frag_counter = hdr-\u003efrag_index_n & 0x3FFF is taken directly from the downlink payload and passed to the decoder, which derives an array index and flash offset as frag_counter - 1. DataFragment fragments are 1-indexed, so a frag_counter of 0 underflows that arithmetic.\n\nWith the default Semtech/LoRaMAC-node decoder, this reaches FragDecoder.FragNbMissingIndex[fragCounter - 1] = 0; in FragDecoderProcess(), where fragCounter - 1 evaluates to -1 and writes a uint16_t zero out of bounds, just before the array and into the adjacent MatrixM2B recovery-matrix state of the static decoder object (CWE-787). A companion write derives a wild flash offset, but that path is rejected by the flash_area_write() bounds check. The in-tree low-memory decoder (frag_dec()) is not corrupted: its out-of-range bit-array and flash accesses are caught by sys_bitarray_ and flash_area_ bounds checks.\n\nThe handler is the registered downlink callback for the fragmentation transport port, reachable whenever an active fragmentation session exists, so the triggering byte is attacker-influenceable LoRaWAN/FUOTA network input. Triggering it requires authenticated downlinks (LoRaWAN MAC session keys or a malicious/compromised network or FUOTA server) and an active fragmentation session. The impact is contained: corruption of decoder state and denial of the firmware-update (FUOTA) session rather than controllable memory corruption or code execution. The fix adds a transport-layer check that rejects frag_counter == 0, closing the defect for both decoder backends.","aliases":["GHSA-fvm7-7whg-8gj6"],"modified":"2026-08-17T04:19:19.301899Z","published":"2026-08-14T17:52:03.680Z","database_specific":{"cwe_ids":["CWE-787"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12363.json","unresolved_ranges":[{"extracted_events":[{"introduced":"3.7.0"},{"fixed":"4.5.0"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"zephyr"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12363.json"},{"type":"ADVISORY","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-fvm7-7whg-8gj6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-12363"},{"type":"FIX","url":"https://github.com/zephyrproject-rtos/zephyr/commit/452c704a28369236e555543c61a1894cd1a4afbb"},{"type":"PACKAGE","url":"https://github.com/zephyrproject-rtos/zephyr"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zephyrproject-rtos/zephyr","events":[{"introduced":"0"},{"fixed":"452c704a28369236e555543c61a1894cd1a4afbb"}],"database_specific":{"source":"REFERENCES"}}],"versions":["v4.4.0","v4.4.0-rc3","v4.4.0-rc2","v4.4.0-rc1","v4.3.0","v4.3.0-rc3","v4.3.0-rc2","v4.3.0-rc1","v4.2.0","v4.2.0-rc3","v4.2.0-rc2","v4.2.0-rc1","v4.1.0","v4.1.0-rc3","v4.1.0-rc2","v4.1.0-rc1","v4.0.0","v4.0.0-rc3","v4.0.0-rc2","v4.0.0-rc1","v3.7.0","v3.7.0-rc3","v3.7.0-rc2","v3.7.0-rc1","v3.6.0","v3.6.0-rc3","v3.6.0-rc2","v3.6.0-rc1","zephyr-v3.5.0","v3.5.0","v3.5.0-rc3","v3.5.0-rc2","v3.5.0-rc1","zephyr-v3.4.0","v3.4.0","v3.4.0-rc3","v3.4.0-rc2","v3.4.0-rc1","zephyr-v3.3.0","v3.3.0","v3.3.0-rc3","v3.3.0-rc2","v3.3.0-rc1","zephyr-v3.2.0","v3.2.0","v3.2.0-rc3","v3.2.0-rc2","v3.2.0-rc1","zephyr-v3.1.0","v3.1.0","v3.1.0-rc3","v3.1.0-rc2","v3.1.0-rc1","zephyr-v3.0.0","v3.0.0","v3.0.0-rc3","v3.0.0-rc2","v3.0.0-rc1","v2.7.99","v2.7.0-rc3","v2.7.0-rc2","v2.7.0-rc1","zephyr-v2.6.0","v2.6.0","v2.6.0-rc3","v2.6.0-rc2","v2.6.0-rc1","zephyr-v2.5.0","v2.5.0","v2.5.0-rc4","v2.5.0-rc3","v2.5.0-rc2","v2.5.0-rc1","zephyr-v2.4.0","v2.4.0","v2.4.0-rc3","v2.4.0-rc2","v2.4.0-rc1","zephyr-v2.3.0","v2.3.0","v2.3.0-rc2","v2.3.0-rc1","zephyr-v2.1.0","v2.1.0","zephyr-v2.2.0","v2.2.0","v2.2.0-rc3","v2.2.0-rc2","v2.2.0-rc1","v2.1.0-rc3","v2.1.0-rc2","v2.1.0-rc1","zephyr-v2.0.0","v2.0.0","v2.0.0-rc3","v2.0.0-rc2","v2.0.0-rc1","zephyr-v1.14.0","v1.14.0","v1.14.0-rc3","v1.14.0-rc2","v1.14.0-rc1","zephyr-v1.13.0","v1.13.0","v1.13.0-rc3","v1.13.0-rc2","v1.13.0-rc1","zephyr-v1.12.0","v1.12.0","v1.12.0-rc3","v1.12.0-rc2","v1.12.0-rc1","zephyr-v1.11.0","v1.11.0","v1.11.0-rc3","v1.11.0-rc2","v1.11.0-rc1","zephyr-v1.10.0","v1.10.0","v1.10.0-rc3","v1.10.0-rc2","v1.10.0-rc1","zephyr-v1.9.0","v1.9.0","v1.9.0-rc4","v1.9.0-rc3","v1.9.0-rc2","v1.9.0-rc1","v1.8.99","zephyr-v1.5.0","v1.5.0","v1.7.99","v1.6.99","v1.5.0-rc4","v1.5.0-rc3","v1.5.0-rc2","v1.5.0-rc1","v1.5.0-rc0","zephyr-v1.4.0","v1.4.0","v1.4.0-rc3","v1.4.0-rc2","v1.4.0-rc1","zephyr-v1.3.0","v1.3.0","v1.3.0-rc2","v1.3.0-rc1","zephyr-v1.2.0","v1.2.0","v1.2.0-rc2","v1.2.0-rc1","zephyr-v1.1.0","v1.1.0","v1.1.0-rc1","zephyr-v1.0.0","v1.0.0"],"database_specific":{"vanir_signatures_modified":"2026-08-17T04:19:19Z","vanir_signatures":[{"deprecated":false,"digest":{"function_hash":"97319000902993210716179108026057840453","length":5417},"id":"CVE-2026-12363-90a2cf5a","signature_type":"Function","signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/452c704a28369236e555543c61a1894cd1a4afbb","target":{"function":"frag_transport_package_callback","file":"subsys/lorawan/services/frag_transport.c"}},{"target":{"file":"subsys/lorawan/services/frag_transport.c"},"deprecated":false,"digest":{"line_hashes":["112845152174828397077883111524002289420","181017200071947815983925304541590839893","311439266199497870871025372808093216087"],"threshold":0.9},"id":"CVE-2026-12363-accecc7d","signature_type":"Line","signature_version":"v1","source":"https://github.com/zephyrproject-rtos/zephyr/commit/452c704a28369236e555543c61a1894cd1a4afbb"}],"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-12363.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L"}]}