ZephyrProject Zephyr up to 4.4.x MCTP mctp_usb.c mctp_usb_class_disable use after free

Summaryinfo

A vulnerability was found in ZephyrProject Zephyr up to 4.4.x. It has been classified as critical. Impacted is the function mctp_usb_class_disable of the file subsys/pmci/mctp/mctp_usb.c of the component MCTP. Performing a manipulation results in use after free. This vulnerability is identified as CVE-2026-85032. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in ZephyrProject Zephyr up to 4.4.x. This affects the function mctp_usb_class_disable of the file subsys/pmci/mctp/mctp_usb.c of the component MCTP. The manipulation with an unknown input leads to a use after free vulnerability. CWE is classifying the issue as CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. This is going to have an impact on integrity, and availability. The summary by CVE is:

The MCTP over USB device class in subsys/pmci/mctp/mctp_usb.c splits RX handling across two threads: the system workqueue runs mctp_usb_class_out_work(), which parses host OUT data byte by byte and fills a packet buffer at usb->rx_pkt, while the USB device stack thread runs mctp_usb_class_disable(). The disable handler used k_work_cancel(), which removes a queued work item but returns immediately without waiting for a handler that is already running, and then called mctp_usb_reset_rx_state() to mctp_pktbuf_free() the packet buffer the worker may still be using. Both entry points into mctp_usb_class_disable() are driven by the attached USB host: a SET_CONFIGURATION request and a USB bus reset both reach it via usbd_config_reset() in subsys/usb/device_next/usbd_config.c. A host that streams partial MCTP frames on the bulk OUT endpoint and repeatedly forces a configuration change or bus reset therefore controls both the data being parsed and the moment the teardown runs, and can retry the race indefinitely without credentials or user interaction. If the free lands while the worker holds the pointer, the worker writes host-supplied bytes into freed memory of the dedicated MCTP heap (CONFIG_MCTP_HEAP_SIZE in subsys/pmci/mctp/mctp_memory.c), corrupting recycled buffers or sys_heap free-block metadata; this window requires genuine parallelism, i.e. CONFIG_SMP or a preemptible CONFIG_SYSTEM_WORKQUEUE_PRIORITY. With the default cooperative workqueue the worker can still yield inside mctp_bus_rx() (application callback or a control-message reply blocking in mctp_usb_tx()), after which it resumes and calls mctp_pktbuf_free(usb->rx_pkt) on a pointer the teardown has NULLed, dereferencing NULL and faulting on targets with null-pointer detection. The fix replaces the cancel with k_work_cancel_sync() plus a new struct k_work_sync out_work_sync, so disable waits for the RX worker to finish before draining the FIFO and freeing the packet buffer. The affected code is the MCTP subsystem, which is marked experimental, built only with CONFIG_MCTP_USB.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-85032 since 09/02/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available.

Upgrading to version 4.5.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• ZephyrProject

Name

• Zephyr

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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