{"id":"CVE-2026-76787","state":"PUBLISHED","title":"NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum","description":"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.","publishedAt":"2026-10-19T20:39:20.425Z","updatedAt":"2026-10-20T18:08:01.790Z","severity":{"score":5.9,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"zephyr"},"assigner":"zephyr","products":["zephyrproject zephyr"],"affected":[{"vendor":"zephyrproject","product":"zephyr","packageName":"zephyr","defaultStatus":"unaffected","versions":[{"version":"2.4.0","status":"affected","lessThan":"4.5.0","versionType":"semver"}],"collectionURL":"https://github.com/zephyrproject-rtos/zephyr","programFiles":["subsys/mgmt/updatehub/updatehub.c"],"programRoutines":[{"name":"z_impl_updatehub_probe"}]}],"references":["https://github.com/zephyrproject-rtos/zephyr/commit/6fc4f27a74021b52c509e4f7912d68145dfa7728","https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2"],"weaknesses":["CWE-476"],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/76xxx/CVE-2026-76787.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-76787","state":"PUBLISHED","datePublished":"2026-10-19T20:39:20.425Z","dateUpdated":"2026-10-20T18:08:01.790Z","assignerShortName":"zephyr","assignerOrgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","dateReserved":"2026-08-19T17:53:24.899Z"},"containers":{"cna":{"title":"NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"zephyrproject","product":"zephyr","packageName":"zephyr","defaultStatus":"unaffected","versions":[{"version":"2.4.0","status":"affected","lessThan":"4.5.0","versionType":"semver"}],"collectionURL":"https://github.com/zephyrproject-rtos/zephyr","programFiles":["subsys/mgmt/updatehub/updatehub.c"],"programRoutines":[{"name":"z_impl_updatehub_probe"}]}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/6fc4f27a74021b52c509e4f7912d68145dfa7728","name":"Fix commit","tags":["patch"]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2","name":"GHSA-82gq-cmqw-xgx2"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":5.9,"baseSeverity":"MEDIUM"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-476","lang":"en","description":"memory-safety","type":"CWE"}]}],"providerMetadata":{"shortName":"zephyr","orgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","dateUpdated":"2026-10-19T20:39:20.425Z"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-76787","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-20T18:04:36.017568Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-20T18:08:01.790Z"}}]}}}