{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-9728","assignerOrgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","state":"PUBLISHED","assignerShortName":"zephyr","dateReserved":"2026-05-27T17:11:30.502Z","datePublished":"2026-08-24T14:28:46.429Z","dateUpdated":"2026-08-25T19:06:35.431Z"},"containers":{"cna":{"providerMetadata":{"orgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","shortName":"zephyr","dateUpdated":"2026-08-24T14:28:46.429Z"},"title":"TOCTOU race in mbox_send syscall verifier allows userspace to leak kernel memory","descriptions":[{"lang":"en","value":"The userspace syscall verifier z_vrfy_mbox_send() in drivers/mbox/mbox_handlers.c validated the nested msg->data/msg->size fields by reading them directly out of live userspace memory, and then forwarded the original, still-mutable userspace struct mbox_msg * pointer to z_impl_mbox_send() and the underlying driver. Between the access check and the driver's use of msg->data, the validated pointer could be replaced, leaving a time-of-check/time-of-use window.\n\nOn a system built with CONFIG_USERSPACE, any unprivileged userspace thread may invoke the mbox_send() system call. A second thread sharing the caller's address space can race to overwrite msg->data with a supervisor (kernel) address after the verifier's bounds check has passed but before the driver dereferences it. The driver then reads from the attacker-chosen address in supervisor context (for example memcpy(&data32, msg->data, msg->size) in the NXP mailbox driver, whose bytes are subsequently emitted to the peer mailbox endpoint).\n\nThe impact is a userspace-to-supervisor access-control bypass: disclosure of kernel memory contents (high confidentiality impact), or, for an invalid/unmapped target address, a faulting kernel read causing denial of service. The fix snapshots the entire struct mbox_msg into a kernel-stack copy with k_usermode_from_copy() and validates and forwards that immutable copy, closing the race."}],"affected":[{"vendor":"zephyrproject","product":"zephyr","collectionURL":"https://github.com/zephyrproject-rtos/zephyr","packageName":"zephyr","defaultStatus":"unaffected","programFiles":["drivers/mbox/mbox_handlers.c"],"versions":[{"version":"3.0.0","status":"affected","versionType":"semver","lessThan":"4.4.2"}]}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/ab35eaccec5976f05c196f176d0c32885754496f","name":"Fix commit","tags":["patch"]},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-47q2-w832-7w67","name":"GHSA-47q2-w832-7w67"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:L","baseScore":6.4,"baseSeverity":"MEDIUM"}}],"problemTypes":[{"descriptions":[{"lang":"en","description":"race","cweId":"CWE-367","type":"CWE"}]}],"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-25T19:06:27.362976Z","id":"CVE-2026-9728","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":"2026-08-25T19:06:35.431Z"}}]}}