# CVE-2026-64186: iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs

> A local attacker with debugfs access could trigger an out-of-bounds read in the AMD IOMMU driver due to improper integer handling, potentially causing information disclosure or system crashes.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/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:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-64186, DEBIAN-CVE-2026-64186, GHSA-398p-2vfw-ch77, UBUNTU-CVE-2026-64186

## What is CVE-2026-64186?

CVE-2026-64186 is a high-severity vulnerability in Linux kernel, published on 19 Jul 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/amd: Remove latent out-of-bounds access in IOMMU debugfs

In iommu_mmio_write() and iommu_capability_write(), the variables
dbg_mmio_offset and dbg_cap_offset are declared as int. However, they
are populated using kstrtou32_from_user(). If a user provides a
sufficiently large value, it can become a negative integer.

Prior to this patch, the AMD IOMMU debugfs implementation was already
protected by different mechanisms.

1. #define OFS_IN_SZ 8 ensures the user string <= 8 bytes, so
   e.g. 0xffffffff isn't a valid input.

  if (cnt > OFS_IN_SZ)
     return -EINVAL;

2. Implicit type promotion in iommu_mmio_write(), dbg_mmio_offset is int
   and iommu->mmio_phys_end is u64

  if (dbg_mmio_offset > iommu->mmio_phys_end - sizeof(u64))
      return -EINVAL;

3. The show handlers would currently catch the negative number and
   refuse to perform the read.

Replace kstrtou32_from_user() with kstrtos32_from_user() to parse the
input, and check for negative values to explicitly prevent out-of-bounds
memory accesses directly in iommu_mmio_write() and
iommu_capability_write().

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-64186?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64186?

Apply the vendor's patch.

## Is CVE-2026-64186 being exploited?

There is no known exploitation of CVE-2026-64186 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64186 and fix it if it is affected.

What it is: CVE-2026-64186 is a high-severity vulnerability in Linux kernel, published on 19 Jul 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-2026-64186 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-64186/ (Markdown: https://insights.sbomify.com/CVE-2026-64186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64186
- OSV: https://osv.dev/vulnerability/CVE-2026-64186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64186/
Summaries are generated and may contain mistakes; the official description above is the record.