# CVE-2026-74573: iommu/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

> A missing check in the Linux kernel's ARM SMMU driver allows out-of-bounds reads or invalidations when devices have zero or multiple streams, potentially causing a crash.

- **Severity:** Critical 9.3 (`CVSS:3.1/AV:L/AC:L/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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-74573, DEBIAN-CVE-2026-74573, GHSA-p5wj-hqvh-c7x4, UBUNTU-CVE-2026-74573

## What is CVE-2026-74573?

CVE-2026-74573 is a critical vulnerability in Linux, published on 15 Aug 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/arm-smmu-v3-iommufd: Require exactly one Stream ID for a vDEVICE

arm_vsmmu_vsid_to_sid() maps a guest's vSID to a single physical Stream ID
taken from master->streams[0], assuming a device has exactly one stream. A
device with several streams gets only its first one mapped, so a guest vSID
invalidation cannot reach the others' ATC and IOTLB entries; a device with
none makes master->streams a ZERO_SIZE_PTR, read out of bounds.

Add an arm_vsmmu_vdevice_init() op to reject the vDEVICE with -EOPNOTSUPP
when master->num_streams is not one, rather than mapping it silently.

## Which versions are affected by CVE-2026-74573?


## How do I fix CVE-2026-74573?

Apply the vendor's patch.

## Is CVE-2026-74573 being exploited?

There is no known exploitation of CVE-2026-74573 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74573 and fix it if it is affected.

What it is: CVE-2026-74573 is a critical vulnerability in Linux, published on 15 Aug 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-2026-74573 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-2026-74573/ (Markdown: https://insights.sbomify.com/CVE-2026-74573/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74573
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74573
- OSV: https://osv.dev/vulnerability/CVE-2026-74573

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74573/
Summaries are generated and may contain mistakes; the official description above is the record.