CVE-2026-90586: Xtensa MMU uninitialized page-table pointer in userspace thread setup

CVE-2026-90586 · Severity: high · CVSS 7.8 · Published 2026-11-09

The Xtensa processor's memory management unit (MMU) in user-mode thread handling fails to initialize a critical pointer, allowing unprivileged users to allocate and manipulate kernel memory structures. An attacker can read and write kernel memory out-of-bounds, leading to kernel panics or complete sandbox escape with full system compromise.

Technologies: Zephyr RTOS. Vendors: Zephyr.

Quick answers

Is CVE-2026-90586 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-90586 being exploited in the wild.
How severe is CVE-2026-90586?
High severity, with a CVSS score of 7.8, published 9 November 2026.
Which products and versions are affected?
Zephyr RTOS Xtensa MMU userspace configurations with CONFIG_XTENSA_MMU and CONFIG_USERSPACE.
Is there a fix for CVE-2026-90586?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-90586 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-90586?
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.

Technical details

The Xtensa MMU userspace port does not zero the thread->arch.ptables field during thread creation, but arch_mem_domain_thread_add() uses a non-NULL value as a predicate for memory domain migration. An attacker exploits this by recycling heap memory through k_object_alloc(K_OBJ_THREAD) to inject stale page-table pointers, triggering unguarded indexing and pointer dereferences in supervisor mode via region_map_update() and dup_l2_table_if_needed(). The vulnerability requires CONFIG_XTENSA_MMU, CONFIG_USERSPACE, and dynamically allocated kernel objects.

Affected products

  • Zephyr Zephyr RTOS Xtensa MMU userspace configurations with CONFIG_XTENSA_MMU and CONFIG_USERSPACE

Timeline

  • 2026-11-09: disclosed

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