{"schema":"threatline.record/2","record":{"id":"CVE-2026-76787","aliases":["GHSA-82gq-cmqw-xgx2"],"summary":"NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum","details":"The UpdateHub firmware-over-the-air client parses the CoAP probe response with Zephyr's JSON library in z_impl_updatehub_probe() (subsys/mgmt/updatehub/updatehub.c). The decoder treats every descriptor field as optional — json_obj_parse() returns a bitmask of the fields it actually decoded and never fails on a missing one — so a response that omits the \"sha256sum\" string leaves the corresponding const char * in the zero-initialised struct resp_probe_any_boards / struct resp_probe_some_boards at NULL. Both metadata branches then computed sha256size = strlen(...objects.sha256sum) + 1 before any validation, dereferencing that NULL pointer; the SHA256_HEX_DIGEST_SIZE test that follows operates on a value the bad read has already produced and cannot prevent it.\n\nThe metadata is supplied entirely by the network peer: probe_cb() accepts the datagram, runs coap_packet_parse() and copies the payload with no token matching and no cryptographic check. With CONFIG_UPDATEHUB_DTLS unset — the default — start_coap_client() uses plain CoAP over UDP on port 5683 with no peer authentication and resolves the server via unauthenticated DNS, so an on-path attacker, a DNS spoofer, or an off-path attacker who wins the race with a forged source address can deliver the malformed metadata. A probe response as simple as \"objects\":[[{}],[{}]] suffices, and no user interaction is required because updatehub_autohandler() polls on CONFIG_UPDATEHUB_POLL_INTERVAL. When CONFIG_UPDATEHUB_DTLS=y the trigger narrows to a malicious or compromised update server.\n\nThe primitive is a read at address zero, not a write, so the impact is availability only. On targets where the low address range is unmapped or protected — MMU-based architectures, builds with CONFIG_NULL_POINTER_EXCEPTION_DETECTION_DWT/_MPU/_PMP, TrustZone non-secure images, and SoCs such as nRF54L whose 0x0–0x400 window is unmapped — the load faults and Zephyr's default fatal handler halts the system, giving a remotely re-triggerable denial of service on every poll. On classic Cortex-M targets where the vector table is readable at address zero the walk usually terminates immediately and the request is rejected by the length check, so the outcome is configuration- and SoC-dependent. There is no memory write, and the copied bytes are only compared against the locally computed image hash, so there is no information-disclosure channel.\n\nThe fix adds an explicit sha256sum == NULL test that returns UPDATEHUB_METADATA_ERROR ahead of the strlen() in both metadata branches. Debug builds (CONFIG_UPDATEHUB_LOG_LEVEL=4) still format the same pointers with %s in a LOG_DBG() loop that runs before the new checks, so that variant remains in debug configurations only.","categories":["Unclassified"],"product":"zephyr","vendor":"zephyrproject","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-76787","source_modified_at":"2026-10-20T18:08:01.790Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"zephyr","vendor":"zephyrproject","versions":[{"lessThan":"4.5.0","status":"affected","version":"2.4.0","versionType":"semver"}],"defaultStatus":"unaffected"},{"source":"GitHub Advisory Database","source_url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2","source_modified_at":"2026-10-19T21:35:05Z","fetched_at":"2026-10-23T18:48:36.087640Z","package":{"ecosystem":"other","name":"zephyr"},"range":">= 2.4.0, <= 4.4.2"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-76787","source_modified_at":"2026-10-20T18:08:01.790Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"zephyr","ecosystem":null},"version":"4.5.0","basis":"first unaffected version stated in the CVE record"},{"source":"GitHub Advisory Database","source_url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2","source_modified_at":"2026-10-19T21:35:05Z","fetched_at":"2026-10-23T18:48:36.087640Z","package":{"ecosystem":"other","name":"zephyr"},"version":"4.5.0"}],"cvss":5.9,"severity":"Medium","kev":{"listed":false},"epss":{"probability":0.00285,"percentile":0.19935,"score_date":"2026-10-23"},"published_at":"2026-10-19T20:39:20.425Z","modified_at":"2026-10-20T18:08:01.790Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-76787","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-20T18:08:01.790Z"},{"source":"GitHub Advisory Database","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2","fetched_at":"2026-10-23T18:48:36.087640Z","source_modified_at":"2026-10-19T21:35:05Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-76787","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","GitHub Advisory Database","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/zephyrproject-rtos/zephyr/commit/6fc4f27a74021b52c509e4f7912d68145dfa7728","tags":["patch"]},{"source":"CVE List","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"partial","assessed_at":"2026-10-20T18:04:36.017568Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-10-20T18:08:01.790Z","content_hash":"7cb43954c697368ebd31aba9c67ded6049be5f0bccb07957d71737628b2cc931"}}