Kernel-memory disclosure via mailbox verifier race
Published Aug 24, 2026 · Updated Aug 24, 2026
TOCTOU race in Zephyr Project Zephyr RTOS 3.0.0 through 4.4.1 allows local users to read kernel memory through mbox_send(). The z_vrfy_mbox_send() verifier checks msg->data and msg->size in mutable userspace memory, then passes the same struct to a driver that dereferences it. Exploitation requires CONFIG_USERSPACE and a second thread to swap the pointer after validation; a successful race discloses supervisor memory, while an invalid address can fault the kernel.
Summary
What happened
TOCTOU race in Zephyr Project Zephyr RTOS 3.0.0 through 4.4.1 allows local users to read kernel memory through mbox_send(). The z_vrfy_mbox_send() verifier checks msg->data and msg->size in mutable userspace memory, then passes the same struct to a driver that dereferences it. Exploitation requires CONFIG_USERSPACE and a second thread to swap the pointer after validation; a successful race discloses supervisor memory, while an invalid address can fault the kernel.
The record
- CVE
- CVE-2026-9728
- Published
- Aug 24, 2026
- Updated
- Aug 24, 2026
- Vendor
- Zephyr Project
- Product
- Zephyr RTOS
- Classifications
- CWE-367, T1005
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 24, 2026CVE publishedPublication date reported by the CVE source.
- Aug 24, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=3.0.0 <4.4.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Zephyr mbox_send TOCTOU proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo