# CVE-2026-79979: Stale TLB entries after demand-paging page-out let arm64 user threads access reused physical frames


- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** GHSA-6pqm-hfxf-48qv, UBUNTU-CVE-2026-79979

## What is CVE-2026-79979?

CVE-2026-79979 is a high-severity vulnerability in zephyrproject zephyr, published on 23 Oct 2026. 

### Official description

The arm64 MMU backend invalidates a single virtual address from the TLB with invalidate_tlb_page() in arch/arm64/core/mmu.c, which issued TLBI VAE1{IS} with an operand of virt >> 12. That operand encodes the ASID in bits [63:48], so the invalidation only ever matched ASID 0 (the kernel page tables) and global entries. Memory domains, however, are allocated ASIDs starting at 1 in arch_mem_domain_init(), and every domain-private leaf created by private_map() is mapped with MT_NG, i.e. non-global. A domain's cached translation therefore survived the invalidation.

All callers of invalidate_tlb_page() are demand-paging paths. When the eviction algorithm reclaims a frame, page_frame_prepare_locked() in kernel/mmu.c calls arch_mem_page_out(), which marks the kernel leaf invalid, propagates the invalid descriptor into every domain via sync_domains(), and then flushes only ASID 0. do_page_fault() immediately reuses the very same page frame for the incoming mapping through arch_mem_page_in(). A user thread that had already touched the evicted page — a k_mem_partition added with arch_mem_domain_partition_add(), or its own stack mapped by map_thread_stack() — retains a valid EL0 read/write translation to that physical frame under its own ASID.

Unprivileged code running in a user thread can drive memory pressure to force eviction and then keep accessing the stale address, obtaining read and write access to whatever the kernel subsequently placed in that frame: supervisor data, another memory domain's partition, or another thread's stack. This defeats the isolation that CONFIG_USERSPACE is meant to enforce, allowing information disclosure and memory corruption up to full compromise of the system.

The fix switches the implementation to TLBI VAAE1{IS}, which matches every ASID and both global and non-global entries, so no domain-tagged translation survives a page out, dirty-bit update or access-flag clear. Exploitation requires an arm64 build with both CONFIG_USERSPACE and CONFIG_DEMAND_PAGING enabled, an active backing store, and at least one demand-paged page that is also privately mapped into a user memory domain. The same commit additionally stops globalize_table() from stripping EL0 permission and non-global attributes off domain-private leaves during paging synchronization, which previously caused user threads to lose access to their own partitions and stacks.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-79979?


## How do I fix CVE-2026-79979?

No fix has been published for CVE-2026-79979 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-79979 being exploited?

There is no known exploitation of CVE-2026-79979 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79979 and fix it if it is affected.

What it is: CVE-2026-79979 is a high-severity vulnerability in zephyrproject zephyr, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-79979 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-2026-79979/ (Markdown: https://insights.sbomify.com/CVE-2026-79979/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79979
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79979
- OSV: https://osv.dev/vulnerability/CVE-2026-79979

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79979/
Summaries are generated and may contain mistakes; the official description above is the record.