# 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.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Oct 2026
- **Updated:** 9 Oct 2026
- **Also known as:** GHSA-923h-8c2j-pcm5

## 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 (Improper Access Control)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-19574 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-19574 in the wild and no public exploit code.

Affected product: zephyrproject zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-19574/ (Markdown: https://insights.sbomify.com/CVE-2026-19574/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-19574
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-19574
- OSV: https://osv.dev/vulnerability/CVE-2026-19574

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-19574/
Summaries are generated and may contain mistakes; the official description above is the record.