{"api_version":"1","generated_at":"2026-10-21T22:12:09+00:00","cve":"CVE-2026-19947","urls":{"html":"https://cve.report/CVE-2026-19947","api":"https://cve.report/api/cve/CVE-2026-19947.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-19947","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-19947"},"summary":{"title":"Missing kernel object permission check in devmux syscalls allows unprivileged user threads to retarget a device multiplexer","description":"The device multiplexer pseudo-driver in drivers/misc/devmux/devmux.c exposes two system calls, devmux_select_get() and devmux_select_set(). When CONFIG_USERSPACE is enabled, their user-mode verifiers z_vrfy_devmux_select_get() and z_vrfy_devmux_select_set() forwarded directly to the kernel implementations without performing any kernel-object validation — no k_object_access_check() and no driver object check. Compounding this, DEVICE_DT_INST_DEFINE() registered devmux instances with a NULL driver API pointer, which causes scripts/build/gen_kobject_list.py to skip them entirely, so a devmux device had no struct k_object and no permission on it could be granted or withheld in the first place.\n\nAny thread running in user mode can reach the defect: device pointers such as DEVICE_DT_GET(DT_NODELABEL(devmux0)) are compile-time constants available to application code, and the syscall accepted them from a thread that had never been granted access to the device. The kernel implementations do validate the pointer against the static devmux instance table and bounds-check the selection index, so this is not a memory-safety issue; the failure is purely one of authorization. Exposure requires CONFIG_USERSPACE=y together with the experimental CONFIG_DEVMUX=y (which depends on CONFIG_DEVICE_MUTABLE) and a zephyr,devmux devicetree node.\n\nAn unprivileged user-mode thread can read and change which downstream device a multiplexer forwards to, bypassing the userspace object-permission model. Because a devmux forwards the data, configuration and API of the selected device — its documented use being zephyr,console and zephyr,shell-uart switching — an attacker can suppress console, log and shell output, redirect that output to a downstream device it is able to observe, or flip the selection underneath another thread that is legitimately using the multiplexer. The impact is bounded to the devicetree-fixed set of downstream devices; no out-of-bounds access or arbitrary pointer dereference is reachable.\n\nThe fix declares __subsystem struct devmux_driver_api and attaches a DEVICE_API(devmux, devmux_api) instance to each devmux device so that it becomes a tracked K_OBJ_DRIVER_DEVMUX kernel object, and adds K_OOPS(devmux_inst_get(dev) == SIZE_MAX) plus K_OOPS(k_object_access_check(dev) != 0) to both verifiers.","state":"PUBLISHED","assigner":"zephyr","published_at":"2026-10-21 19:17:02","updated_at":"2026-10-21 19:17:02"},"problem_types":["CWE-862","CWE-862 auth"],"metrics":[{"version":"3.1","source":"vulnerabilities@zephyrproject.org","type":"Secondary","score":"5.3","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","baseScore":5.3,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"LOW"}},{"version":"3.1","source":"CNA","type":"CVSS","score":"5.3","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","data":{"baseScore":5.3,"baseSeverity":"MEDIUM","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","version":"3.1"}}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-8m8g-f5jf-x28x","name":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-8m8g-f5jf-x28x","refsource":"vulnerabilities@zephyrproject.org","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/4b7f98345d8f894f4b8aabe52a2623d843669fac","name":"https://github.com/zephyrproject-rtos/zephyr/commit/4b7f98345d8f894f4b8aabe52a2623d843669fac","refsource":"vulnerabilities@zephyrproject.org","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-19947","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-19947","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"zephyrproject","product":"zephyr","version":"affected 3.6.0 4.5.0 semver","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"collectionURL":"https://github.com/zephyrproject-rtos/zephyr","defaultStatus":"unaffected","packageName":"zephyr","product":"zephyr","programFiles":["drivers/misc/devmux/devmux.c","include/zephyr/drivers/misc/devmux/devmux.h"],"programRoutines":[{"name":"z_vrfy_devmux_select_get"},{"name":"z_vrfy_devmux_select_set"}],"vendor":"zephyrproject","versions":[{"lessThan":"4.5.0","status":"affected","version":"3.6.0","versionType":"semver"}]}],"descriptions":[{"lang":"en","value":"The device multiplexer pseudo-driver in drivers/misc/devmux/devmux.c exposes two system calls, devmux_select_get() and devmux_select_set(). When CONFIG_USERSPACE is enabled, their user-mode verifiers z_vrfy_devmux_select_get() and z_vrfy_devmux_select_set() forwarded directly to the kernel implementations without performing any kernel-object validation — no k_object_access_check() and no driver object check. Compounding this, DEVICE_DT_INST_DEFINE() registered devmux instances with a NULL driver API pointer, which causes scripts/build/gen_kobject_list.py to skip them entirely, so a devmux device had no struct k_object and no permission on it could be granted or withheld in the first place.\n\nAny thread running in user mode can reach the defect: device pointers such as DEVICE_DT_GET(DT_NODELABEL(devmux0)) are compile-time constants available to application code, and the syscall accepted them from a thread that had never been granted access to the device. The kernel implementations do validate the pointer against the static devmux instance table and bounds-check the selection index, so this is not a memory-safety issue; the failure is purely one of authorization. Exposure requires CONFIG_USERSPACE=y together with the experimental CONFIG_DEVMUX=y (which depends on CONFIG_DEVICE_MUTABLE) and a zephyr,devmux devicetree node.\n\nAn unprivileged user-mode thread can read and change which downstream device a multiplexer forwards to, bypassing the userspace object-permission model. Because a devmux forwards the data, configuration and API of the selected device — its documented use being zephyr,console and zephyr,shell-uart switching — an attacker can suppress console, log and shell output, redirect that output to a downstream device it is able to observe, or flip the selection underneath another thread that is legitimately using the multiplexer. The impact is bounded to the devicetree-fixed set of downstream devices; no out-of-bounds access or arbitrary pointer dereference is reachable.\n\nThe fix declares __subsystem struct devmux_driver_api and attaches a DEVICE_API(devmux, devmux_api) instance to each devmux device so that it becomes a tracked K_OBJ_DRIVER_DEVMUX kernel object, and adds K_OOPS(devmux_inst_get(dev) == SIZE_MAX) plus K_OOPS(k_object_access_check(dev) != 0) to both verifiers."}],"metrics":[{"cvssV3_1":{"baseScore":5.3,"baseSeverity":"MEDIUM","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","version":"3.1"},"format":"CVSS"}],"problemTypes":[{"descriptions":[{"cweId":"CWE-862","description":"auth","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-10-21T18:19:35.637Z","orgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","shortName":"zephyr"},"references":[{"name":"Fix commit","tags":["patch"],"url":"https://github.com/zephyrproject-rtos/zephyr/commit/4b7f98345d8f894f4b8aabe52a2623d843669fac"},{"name":"GHSA-8m8g-f5jf-x28x","url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-8m8g-f5jf-x28x"}],"title":"Missing kernel object permission check in devmux syscalls allows unprivileged user threads to retarget a device multiplexer","x_generator":{"engine":"cvelib 1.8.0"}}},"cveMetadata":{"assignerOrgId":"e2e69745-5e70-4e92-8431-deb5529a81ad","assignerShortName":"zephyr","cveId":"CVE-2026-19947","datePublished":"2026-10-21T18:19:35.637Z","dateReserved":"2026-08-15T18:43:26.567Z","dateUpdated":"2026-10-21T18:19:35.637Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-21 19:17:02","lastModifiedDate":"2026-10-21 19:17:02","problem_types":["CWE-862","CWE-862 auth"],"metrics":{"cvssMetricV31":[{"source":"vulnerabilities@zephyrproject.org","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L","baseScore":5.3,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"LOW","availabilityImpact":"LOW"},"exploitabilityScore":1.8,"impactScore":3.4}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"19947","Ordinal":"1","Title":"Missing kernel object permission check in devmux syscalls allows","CVE":"CVE-2026-19947","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"19947","Ordinal":"1","NoteData":"The device multiplexer pseudo-driver in drivers/misc/devmux/devmux.c exposes two system calls, devmux_select_get() and devmux_select_set(). When CONFIG_USERSPACE is enabled, their user-mode verifiers z_vrfy_devmux_select_get() and z_vrfy_devmux_select_set() forwarded directly to the kernel implementations without performing any kernel-object validation — no k_object_access_check() and no driver object check. Compounding this, DEVICE_DT_INST_DEFINE() registered devmux instances with a NULL driver API pointer, which causes scripts/build/gen_kobject_list.py to skip them entirely, so a devmux device had no struct k_object and no permission on it could be granted or withheld in the first place.\n\nAny thread running in user mode can reach the defect: device pointers such as DEVICE_DT_GET(DT_NODELABEL(devmux0)) are compile-time constants available to application code, and the syscall accepted them from a thread that had never been granted access to the device. The kernel implementations do validate the pointer against the static devmux instance table and bounds-check the selection index, so this is not a memory-safety issue; the failure is purely one of authorization. Exposure requires CONFIG_USERSPACE=y together with the experimental CONFIG_DEVMUX=y (which depends on CONFIG_DEVICE_MUTABLE) and a zephyr,devmux devicetree node.\n\nAn unprivileged user-mode thread can read and change which downstream device a multiplexer forwards to, bypassing the userspace object-permission model. Because a devmux forwards the data, configuration and API of the selected device — its documented use being zephyr,console and zephyr,shell-uart switching — an attacker can suppress console, log and shell output, redirect that output to a downstream device it is able to observe, or flip the selection underneath another thread that is legitimately using the multiplexer. The impact is bounded to the devicetree-fixed set of downstream devices; no out-of-bounds access or arbitrary pointer dereference is reachable.\n\nThe fix declares __subsystem struct devmux_driver_api and attaches a DEVICE_API(devmux, devmux_api) instance to each devmux device so that it becomes a tracked K_OBJ_DRIVER_DEVMUX kernel object, and adds K_OOPS(devmux_inst_get(dev) == SIZE_MAX) plus K_OOPS(k_object_access_check(dev) != 0) to both verifiers.","Type":"Description","Title":"Missing kernel object permission check in devmux syscalls allows"}]}}}