CVE-2026-19947 zephyrproject CVE debrief

Who should care

Defenders responsible for Zephyr-based systems, particularly those using the device multiplexer pseudo-driver, should assess exposure and prioritize patching. This includes reviewing system configurations, identifying potential vulnerabilities, and implementing necessary security measures to prevent exploitation. Additionally, defenders should monitor for potential unauthorized access and verify the application of patches to ensure the security of their

Why it matters

CVE-2026-19947 allows unprivileged user threads to retarget device multiplexers in Zephyr due to missing kernel object permission checks. Defenders should verify and apply patches, assess exposure, and monitor for potential unauthorized access.

• Unprivileged user threads can retarget device multiplexers, potentially allowing unauthorized access.
• Verification of patch application is necessary to prevent exploitation.
• Exposure assessment is required for systems using affected Zephyr versions.

Technical summary

The device multiplexer pseudo-driver in Zephyr's drivers/misc/devmux/devmux.c has two system calls, devmux_select_get() and devmux_select_set(), that do not perform kernel-object validation when CONFIG_USERSPACE is enabled. This allows unprivileged user threads to retarget a device multiplexer. The issue is due to missing kernel object permission checks, which enables unprivileged user threads to access and control device multiplexers without proper authorization. Defenders should verify and apply patches, assess exposure, and monitor for potential unauthorized access.

Defensive priority

Defenders should prioritize verifying and applying patches for Zephyr versions 3.6.0 up to but not including 4.5.0, and assess exposure in their systems.

Recommended defensive actions

• Verify and apply patches for Zephyr versions 3.6.0 up to but not including 4.5.0
• Assess exposure in systems using Zephyr's device multiplexer pseudo-driver
• Monitor for potential unauthorized access to device multiplexers
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details on the vulnerability, including its description, affected versions, and references to patches and advisories. The source code review indicates that 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

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.