CVE-2026-76787 Desreferencia de puntero NULL en el cliente FOTA UpdateHub al omitir sha256sum

Qué es CVE-2026-76787

El cliente firmware-over-the-air UpdateHub, en z_impl_updatehub_probe(), trata todos los campos del descriptor como opcionales, por lo que una respuesta de sondeo que omite "sha256sum" deja el puntero correspondiente en NULL. Ambas ramas de metadatos calculan strlen() sobre ese puntero antes de validarlo, provocando una desreferencia de puntero NULL. Los metadatos son provistos por el par de red.

Productos y versiones afectadas

• zephyrproject zephyr

  • desde 2.4.0 hasta antes de 4.5.0

Qué hacer

1. Verificá si usás zephyr y en qué versión: el rango afectado figura arriba.
2. Actualizá a la versión corregida que indique el fabricante en su aviso (ver referencias) o aplicá la mitigación que publique.
3. Revisá registros y accesos de los sistemas expuestos para descartar que se haya aprovechado antes de corregir.

Calculadora CVSS

CVSS 3.1 · 5.9 MEDIA

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

VECTOR DE ATAQUE (AV)

Red

COMPLEJIDAD DEL ATAQUE (AC)

Alta

PRIVILEGIOS REQUERIDOS (PR)

Ninguno

INTERACCIÓN DEL USUARIO (UI)

Ninguna

ALCANCE (S)

Sin cambio

CONFIDENCIALIDAD (C)

Ninguna

INTEGRIDAD (I)

Ninguna

DISPONIBILIDAD (A)

Alta

Abrir la calculadora completa →

Descripción original

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. The 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. The 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. The 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.

Referencias

• github.com/zephyrproject-rtos/zephyr/commit/6fc4f27a74021b52c509e4f7912d68145dfa7728PATCH
• github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-82gq-cmqw-xgx2

Historial de la alerta

1. 19 OCT · 19:16VULNERABILIDAD Nueva vulnerabilidad detectada.

CÓMO SE HIZOResumen traducido automáticamente al español a partir de la descripción original. Ante dudas, la descripción original y las referencias del fabricante son la fuente de verdad. Cómo funciona.