# CVE-2026-10669: Xtensa MPU `arch_buffer_validate()` integer-overflow lets a user thread bypass syscall pointer validation

Status: published. Published: 2026-07-14. Updated: 2026-11-04.

On Xtensa SoCs built with CONFIG_XTENSA_MPU and CONFIG_USERSPACE, arch_buffer_validate() in arch/xtensa/core/mpu.c — the architecture hook that verifies a user-mode-supplied buffer is accessible to the calling user thread with the requested permission — defaulted its return value to 0 (access permitted) and only set a denial result inside its per-MPU-region probe loop. When the rounded extent of the buffer wraps the 32-bit address space (size + alignment offset near SIZE_MAX, or ROUND_UP(size + offset) overflowing to 0), the loop executes zero iterations and the function returns 0 = permitted without probing any MPU region.

The syscall-layer pre-checks (K_SYSCALL_MEMORY_SIZE_CHECK / Z_DETECT_POINTER_OVERFLOW) only catch a raw addr+size wrap and do not cover the ROUND_UP-induced wrap, and the string path (arch_user_string_nlen -> arch_buffer_validate) has no syscall-layer guard at all.

An unprivileged user-mode thread can therefore pass a crafted (addr, size) to any syscall that validates user buffers via k_usermode_from_copy/to_copy or k_usermode_string_copy and have validation succeed for memory it must not access; the kernel then reads from (disclosure) or, with write=1, writes to (corruption) attacker-chosen kernel or other-partition memory on the thread's behalf, enabling information disclosure, memory corruption, privilege escalation, and denial of service.

Affected from v3.7.0 (when Xtensa MPU userspace support was added) through v4.4.0. The fix changes the default to -EINVAL (deny by default), adds an explicit size_add_overflow check, and sets the success value only after the full range has been validated.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/zephyrproject-rtos/zephyr/commit/3b1bdaf5482188ca110ef9a411aaa8c7d3db3b16

## Affected products and versions

- zephyrproject / zephyr (zephyr): ≥ 3.7.0; < 4.3.1 (affected, semver); ≥ 4.4.0; < 4.4.1 (affected, semver). Source: CNA: zephyr

## Severity and prioritization

- CVSS 3.1: 7.8 (high); CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H; source: CNA: zephyr

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-03; percentile 7.30%

- SSVC: exploitation none; automatable no; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/zephyrproject-rtos/zephyr/commit/3b1bdaf5482188ca110ef9a411aaa8c7d3db3b16 (CNA: zephyr; patch)

- https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-4r4p-gh69-v6w4 (CNA: zephyr)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-10669; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-10669; retrieved 2026-11-04; source updated Not reported

Revision: f402f9db76a3188f33e57fd9d114fb9741b43653b658ab9ab2f5ecd1c343b538

Canonical: https://y2.dev/cve/CVE-2026-10669

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