CVE-2026-19574 ARM64 MMU can assign an in-use ASID to a new memory domain, breaking user-mode memory isolation
An attacker with supervisor privileges can create many memory domains to cause ASID collisions, allowing user-mode threads to bypass isolation and access other domains' memory.
- 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-2026-19574?
CVE-2026-19574 is a high-severity vulnerability in zephyrproject zephyr, published on 9 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
The ARM64 MMU back-end allocated address space identifiers (ASIDs) for memory domains with a bare round-robin counter in arch_mem_domain_init() (arch/arm64/core/mmu.c). VM_ASID_BITS is 8, so only 255 ASIDs exist; once the counter wrapped, arch_mem_domain_init() could hand an ASID to a new domain while a still-live domain held the same one. Domain-private mappings are installed non-global (MT_NG), so the ASID is the only tag separating one domain's cached translations from another's in the TLB.
The context-switch path in z_arm64_swap_ptables() only flushes the TLB when the outgoing and incoming domains carry the same ASID, which does not cover a duplicate reached through a third domain: for domains A and C sharing an ASID and an unrelated domain B, the schedule A -> B -> C never takes the flush branch, so the ASID-tagged entries A populated remain resident while C runs. Under SMP two live domains sharing an ASID can additionally be resident on two CPUs at once, which the architecture does not allow for distinct translation-table sets.
Triggering the wrap requires a CONFIG_USERSPACE application on ARM64 that creates more than 255 memory domains over its lifetime; k_mem_domain_init() and k_mem_domain_deinit() are supervisor-only APIs and are not exposed as syscalls, so an unprivileged thread cannot drive the counter directly. Once two live domains alias, however, a user-mode thread in one domain can read and write memory belonging to the other domain's partitions and thread stacks with that domain's permissions, defeating the memory-domain isolation boundary.
The fix scans the live domain_list before assigning an ASID, advances the round-robin counter past ASIDs already in use, and returns -ENOMEM when all are taken, so domain creation fails closed instead of silently aliasing.
Weakness: CWE-284
Which versions are affected by CVE-2026-19574?
How do I fix CVE-2026-19574?
No fix has been published for CVE-2026-19574 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19574 being exploited?
There is no known exploitation of CVE-2026-19574 in the wild and no public exploit code.
Sources
Also known as GHSA-923h-8c2j-pcm5.