CVE-2026-10681 Race condition in zephyr
Concurrent thread allocation in Zephyr RTOS allows user threads to share permission slots, bypassing kernel object access controls and enabling privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-10681?
CVE-2026-10681 is a medium-severity vulnerability in Zephyrproject Zephyr, published on 25 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In Zephyr's userspace dynamic-objects subsystem, thread_idx_alloc() in kernel/userspace/userspace.c allocated a new thread permission index from the global _thread_idx_map[] bitmap without holding lists_lock.
On SMP systems, two user-mode threads invoking the k_object_alloc(K_OBJ_THREAD) syscall concurrently can both observe the same low free bit, perform the same non-atomic RMW to clear it, and return the identical tidx.
The two newly created K_OBJ_THREAD objects are then assigned the same thread_id, so the two user threads alias a single bit position in every kernel object's perms[] bitfield: any subsequent grant of access on a kernel object to one thread is implicitly a grant to the other, defeating userspace ACL isolation. A secondary lost-update window between the unlocked &=~BIT() in alloc and the locked |= BIT() in thread_idx_free() can also leak entries from the thread-index pool.
The defect is reachable from any user-mode thread via the unrestricted __syscall k_object_alloc and is gated on CONFIG_USERSPACE, CONFIG_DYNAMIC_OBJECTS, and CONFIG_SMP. The flaw was introduced when the per-thread permission index was added in 2018 and is present in every release up to and including v4.4.0. Fixed by holding lists_lock across the bitmap RMW and the permissions clear (and inlining the obj_list traversal that previously took the lock itself).
Weakness: CWE-362
Which versions are affected by CVE-2026-10681?
It affects 1 product.
Products include Zephyrproject Zephyr.
How do I fix CVE-2026-10681?
No fix has been published for CVE-2026-10681 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-10681 being exploited?
There is no known exploitation of CVE-2026-10681 in the wild and no public exploit code.
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- CVE-2018-1000800 Null dereference in n/a
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Sources
Also known as GHSA-j693-5rh5-8g8h.