CVE-2026-85032

What it 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.

At a glance

Exploitability

Can be exploited with physical access without logging in. High risk of service disruption.

Exploit odds

0.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-09-02 20:23 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-11-03 14:17 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-11-03 19:18 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.2% in the next 30 days (EPSS).
• Severity: 4.8 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-11-03 14:17 UTC

Last modified

2026-11-03 19:18 UTC

Exploit probability

0.2% · EPSS, next 30 days

Weakness

CWE-416 · Use after free

Record status

Awaiting Analysis

Attack profile CVSS 3.1 · 4.8

Attack vector

Physical

Complexity

High

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-85032.md and follow it. Check whether this project is affected by CVE-2026-85032. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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