CVE-2026-19947 (GCVE-0-2026-19947)
Vulnerability from cvelistv5
Published
2026-10-21 18:19
Modified
2026-10-23 21:23
Severity ?
VLAI Severity ?
EPSS score ?
CWE
- CWE-862 - auth
Summary
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.
Any 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.
An 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.
The 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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| zephyrproject | zephyr |
Version: 3.6.0 ≤ |
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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