CVE-2026-85032: Use-after-free in the MCTP over USB binding when the host disables the class while RX parsing is in progress
Noroxi assessment
Priority: Monitor (action score 19/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
- Physical access to the device is required. No account or password is required. No user action is required. Special conditions such as timing or configuration are required.
- Fixed version: zephyrproject zephyr 4.5.0.
Low priority for now. Upgrade to zephyrproject zephyr 4.5.0 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- Nov 3, 2026
- Updated
- Nov 3, 2026
- EPSS
- 0.1% · 7th percentile
- CWE
- CWE-416
Report tools
Action score
19
Monitor
Low priority for now.
- CVSS
- 19 / 40 · 4.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.1%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · zephyr
- 4.8
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
—
Versions reported by the vendor
Affected version ranges reported by the assigning authority (zephyr). Independent of NVD's CPE analysis and usually ahead of it.
zephyrproject zephyr
- 4.4.0 and later · before 4.5.0affected · semver
Same product
zephyrproject: all recordsOther highest-scoring records for the same primary product.
- CVE-2023-4260Potential off-by-one buffer overflow vulnerability in the Zephyr FS subsystem40Plan
- CVE-2021-3625Buffer overflow in Zephyr USB DFU DNLOAD40Plan
- CVE-2020-10071Insufficient publish message length validation in MQTT40Plan
Published before and after this one in the same product
- ← EarlierCVE-2026-82961Oct 28, 2026 · Unvalidated pin index in GPIO syscall handlers allows out-of-bounds kernel writes from user mode31Monitor
- ← EarlierCVE-2026-82962Oct 28, 2026 · Out-of-bounds write in Zephyr Ethernet L2 when adding the link-layer header to a forwarded packet26Monitor
- Later →CVE-2026-85033Nov 3, 2026 · Bluetooth Classic AVRCP Target: missing TX cleanup on disconnect permanently stalls vendor-dependent responses and leaks them to the next peer18Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| zephyrproject zephyr | 4.5.0 | Vendor (CNA) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- Published
- Fix recordedsame day
- TodayNov 10, 2026+7 d
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
- CVE-2026-850350 days apartUse-after-free via dynamically allocated message queue retained by the CAN RX filter35Monitor
- CVE-2026-1236681 days apartUse-after-free freeing an armed dynamically-allocated k_timer in Zephyr userspace object disposal35Monitor
- CVE-2026-7997911 days apartStale TLB entries after demand-paging page-out let arm64 user threads access reused physical frames31Monitor
- CVE-2026-10667114 days apartSMP use-after-free in Zephyr `CONFIG_USERSPACE` dynamic kernel-object tracking, reachable from unprivileged user threads31Monitor
- CVE-2026-1993523 days apartUse-after-free of an L2CAP CoC channel object in the Zephyr Bluetooth host: RX work item is not cancelled on channel teardown30Monitor
- CVE-2026-1068595 days apartUse-after-free of GATT subscribe params in Bluetooth host CCC-write response handler30Monitor
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Physical access to the device is required.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- none
- Integrity
- low · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Physical
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- Low
- Availability impact
- High
Weakness class (CWE)
CWE-416 · Use After FreeCVSS vector
CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
nvd-secondary
Root cause
After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.
The bug in code
The whole CWE-416 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
free(dev->buf);
/* ... another thread is still running ... */
process(dev->buf);Fixed
lock(&dev->lock);
free(dev->buf);
dev->buf = NULL;
unlock(&dev->lock);Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
- SSVC exploitation— → none
- Exploit maturity— → none
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (1 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.