# CVE-2025-39961: iommu/amd/pgtbl: Fix possible race while increase page table level

> A race condition in the AMD IOMMU driver can cause unmap operations to fail, potentially leading to denial of service.

- **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:** 9 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-68348, AZL-76434, BELL-CVE-2025-39961, DEBIAN-CVE-2025-39961, GHSA-cq2w-q6m3-mhw9, ROOT-OS-DEBIAN-11-CVE-2025-39961, ROOT-OS-DEBIAN-12-CVE-2025-39961, ROOT-OS-DEBIAN-13-CVE-2025-39961, ROOT-OS-UBUNTU-2204-CVE-2025-39961, ROOT-OS-UBUNTU-2404-CVE-2025-39961, UBUNTU-CVE-2025-39961

## What is CVE-2025-39961?

CVE-2025-39961 is a high-severity vulnerability in Linux kernel, published on 9 Oct 2025. 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/pgtbl: Fix possible race while increase page table level

The AMD IOMMU host page table implementation supports dynamic page table levels
(up to 6 levels), starting with a 3-level configuration that expands based on
IOVA address. The kernel maintains a root pointer and current page table level
to enable proper page table walks in alloc_pte()/fetch_pte() operations.

The IOMMU IOVA allocator initially starts with 32-bit address and onces its
exhuasted it switches to 64-bit address (max address is determined based
on IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU
driver increases page table level.

But in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads
pgtable->[root/mode] without lock. So its possible that in exteme corner case,
when increase_address_space() is updating pgtable->[root/mode], fetch_pte()
reads wrong page table level (pgtable->mode). It does compare the value with
level encoded in page table and returns NULL. This will result is
iommu_unmap ops to fail and upper layer may retry/log WARN_ON.

CPU 0                                         CPU 1
------                                       ------
map pages                                    unmap pages
alloc_pte() -> increase_address_space()      iommu_v1_unmap_pages() -> fetch_pte()
  pgtable->root = pte (new root value)
                                             READ pgtable->[mode/root]
					       Reads new root, old mode
  Updates mode (pgtable->mode += 1)

Since Page table level updates are infrequent and already synchronized with a
spinlock, implement seqcount to enable lock-free read operations on the read path.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-39961?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39961?

Apply the vendor's patch.

## Is CVE-2025-39961 being exploited?

There is no known exploitation of CVE-2025-39961 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-2025-39961 and fix it if it is affected.

What it is: CVE-2025-39961 is a high-severity vulnerability in Linux kernel, published on 9 Oct 2025. 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-2025-39961 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-2025-39961/ (Markdown: https://insights.sbomify.com/CVE-2025-39961/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39961
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39961
- OSV: https://osv.dev/vulnerability/CVE-2025-39961

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39961/
Summaries are generated and may contain mistakes; the official description above is the record.