# CVE-2026-90243: iommu/vt-d: Clear Present bit before tearing down copied context entry

> A race condition in the Linux kernel IOMMU driver allows hardware to fetch torn context entries, potentially causing spurious faults or system instability.

- **Severity:** High 8.1 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-90243, DEBIAN-CVE-2026-90243, GHSA-h7vj-5r6r-3r99, UBUNTU-CVE-2026-90243

## What is CVE-2026-90243?

CVE-2026-90243 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

iommu/vt-d: Clear Present bit before tearing down copied context entry

copied_context_tear_down() zeroes the 128-bit context entry with
context_clear_entry() while the Present bit is still set, and only then
issues the context-cache and IOTLB invalidations.  This leaves a window
in which hardware can fetch a torn entry, with some fields already zeroed
while Present is still set, leading to unpredictable behaviour or
spurious faults.  While x86 provides strong write ordering, the compiler
may reorder the writes to the two 64-bit halves of the entry, and the
hardware fetch is not guaranteed to be atomic with respect to multiple
CPU writes.

There is no cacheline flush before the invalidation either, so on an
IOMMU without coherent access to the context table the zeroed entry may
not be visible to hardware at the point the invalidation is submitted.

Apply the same ownership handshake described in the VT-d spec, Section
6.5.3.3 ("Guidance to Software for Invalidations"): clear only the Present
bit, flush it out to the IOMMU, perform the invalidations, and only then
zero the remainder of the entry.

## Which versions are affected by CVE-2026-90243?


## How do I fix CVE-2026-90243?

Apply the vendor's patch.

## Is CVE-2026-90243 being exploited?

There is no known exploitation of CVE-2026-90243 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90243 and fix it if it is affected.

What it is: CVE-2026-90243 is a high-severity vulnerability in Linux, published on 17 Sep 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-2026-90243 in the wild and no public exploit code.

Affected product: Linux. 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-2026-90243/ (Markdown: https://insights.sbomify.com/CVE-2026-90243/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90243
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90243
- OSV: https://osv.dev/vulnerability/CVE-2026-90243

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90243/
Summaries are generated and may contain mistakes; the official description above is the record.