CVE-2026-76787 — NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Zephyrproject Zephyr).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Zephyrproject | Zephyr | ≥ 2.4.0 and < 4.5.0 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 5.9 | CVSS 3.1 | Medium | 2.2 | 3.6 | vulnerabilities@zephyrproject.org via NIST National Vulnerability Database |
| 5.9 | CVSS 3.1 | Medium | — | — | zephyr via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: vulnerabilities@zephyrproject.org) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Source status changed · Published → Received
- Record published
- CVSS changed · 5.9
- Source status changed · → Published
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 19, 2026 – Oct 19, 2026
References
2 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-77684 Bluetooth Classic HFP Hands-Free: TX buffer leak on RFCOMM disconnect leads to permanent Bluetooth denial of service 3h
- Medium CVE-2026-19595 Zephyr RTIO syscall verifier validates output parameters for read instead of write access 3h
- High CVE-2026-76788 Stack out-of-bounds write in the OSDP Control Panel reply parser 5h
- Medium CVE-2026-75083 Integer underflow of the radio-reported frame length causes an out-of-bounds write in the NXP KW41Z IEEE 802.15.4 driver 5d
- Medium CVE-2026-75084 Out-of-bounds write in the TI CC1200 IEEE 802.15.4 driver from an unvalidated radio-supplied packet length 5d
- Medium CVE-2026-75085 Out-of-bounds read from received-frame length underflow in the STM32WBA IEEE 802.15.4 driver 5d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No FIRST EPSS score.
- No fixed version, patch or mitigation documented.
- No CISA SSVC assessment.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-76787 is "NULL pointer dereference in the UpdateHub FOTA client when probe metadata omits sha256sum", rated Medium. It affects Zephyr (Zephyrproject); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.9 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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