# CVE-2026-87041: Zephyr RTIO submission-queue verifier memory access bypass

Source: https://junglewise.ai/threats/cve-2026-87041-the-rtio-submission-queue-verifier-rtio-vrfy-sqe-in-subsys-rtio  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-04. Updated: 2026-11-04  
License: CC BY 4.0 with a link back

CVE-2026-87041 · Severity: high · CVSS 7.8 · Published 2026-11-04

Zephyr's RTIO (Real-Time I/O) subsystem contains a logic flaw in the submission-queue verifier that inverts memory permission checks, allowing authorized user threads to read or write arbitrary kernel memory through I2C, I3C, and SPI operations. This breaks the kernel's user-mode isolation boundary and enables attackers to leak sensitive kernel data or corrupt kernel state.

Technologies: [Zephyr RTOS](https://junglewise.ai/threats/technologies/rtos). Vendors: [Zephyr](https://junglewise.ai/threats/vendors/zephyr).

## Quick answers

**Is CVE-2026-87041 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-87041 being exploited in the wild.

**How severe is CVE-2026-87041?** High severity, with a CVSS score of 7.8, published 4 November 2026.

**Which products and versions are affected?** Zephyr RTOS before 4.3.0.

**Is there a fix for CVE-2026-87041?** Yes: fixed in Zephyr 4.3.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-87041 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-87041?** Check whether you run Zephyr RTOS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Zephyr 4.3.0

## Technical details

The rtio_vrfy_sqe() function in subsys/rtio accumulates K_SYSCALL_MEMORY() permission check results using bitwise AND on inverted logic, causing rejection of valid buffers and acceptance of invalid ones. A user-mode thread with RTIO context permissions can submit an SQE (submission queue entry) with a crafted buffer pointer targeting arbitrary kernel memory; downstream I2C, I3C, and SPI RTIO handlers dereference this pointer with supervisor privilege, enabling kernel memory reads (RTIO_OP_TX) or writes (RTIO_OP_RX).

## Affected products

- Zephyr Zephyr RTOS before 4.3.0

## Timeline

- 2026-11-04: disclosed

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