# CVE-2026-79609: x86: XPTI may break on huge-memory systems

> Xen hypervisor fails to apply Meltdown mitigation on systems with memory above 5 TiB, allowing potential information disclosure.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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:** Yes
- **Published:** 13 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** ALPINE-CVE-2026-79609, DEBIAN-CVE-2026-79609, GHSA-842c-7fjj-j8jj, UBUNTU-CVE-2026-79609

## What is CVE-2026-79609?

CVE-2026-79609 is a high-severity vulnerability in Xen, published on 13 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

XPTI (Xen Page Table Isolation) was introduced to mitigate Meltdown
(CVE-2017-5754, one aspect of XSA-254).  This involves copying 64-bit PV
guest page table entries from guest-chosen root page tables to the Xen-
chosen one which is in actual use by hardware.  To read the guest root
page table, the directmap is used.  PV guests, however, have a directmap
which may not cover all memory; in particular this is the case if any
memory extends beyond the 5 TiB (CONFIG_BIGMEM=y: 3.5 TiB) address
boundary.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2026-79609?


## How do I fix CVE-2026-79609?

Apply the vendor's patch.

## Is CVE-2026-79609 being exploited?

There is no known exploitation of CVE-2026-79609 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-79609 and fix it if it is affected.

What it is: CVE-2026-79609 is a high-severity vulnerability in Xen, published on 13 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-2026-79609 in the wild and no public exploit code.

Affected product: Xen. 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-2026-79609/ (Markdown: https://insights.sbomify.com/CVE-2026-79609/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-79609
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-79609
- OSV: https://osv.dev/vulnerability/CVE-2026-79609

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-79609/
Summaries are generated and may contain mistakes; the official description above is the record.