{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-12363","assignerOrgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","state":"PUBLISHED","assignerShortName":"zephyr","dateReserved":"2026-06-16T03:53:41.904Z","datePublished":"2026-08-14T17:52:03.680Z","dateUpdated":"2026-08-14T19:26:51.474Z"},"containers":{"cna":{"providerMetadata":{"orgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","shortName":"zephyr","dateUpdated":"2026-08-14T17:52:03.680Z"},"title":"Out-of-bounds write in LoRaWAN fragmented transport from a fragment index of 0","descriptions":[{"lang":"en","value":"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->frag_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."}],"affected":[{"vendor":"zephyrproject","product":"zephyr","collectionURL":"https://github.com/zephyrproject-rtos/zephyr","packageName":"zephyr","defaultStatus":"unaffected","programFiles":["subsys/lorawan/services/frag_transport.c"],"versions":[{"version":"3.7.0","status":"affected","lessThan":"4.5.0","versionType":"semver"}]}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/452c704a28369236e555543c61a1894cd1a4afbb","name":"Fix commit","tags":["patch"]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-fvm7-7whg-8gj6","name":"GHSA-fvm7-7whg-8gj6"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L","baseScore":4.2,"baseSeverity":"MEDIUM"}}],"problemTypes":[{"descriptions":[{"lang":"en","description":"bounds","cweId":"CWE-787","type":"CWE"}]}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-14T19:26:34.004071Z","id":"CVE-2026-12363","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-08-14T19:26:51.474Z"}}]}}