---
title: "HOST-KRN-028 Unprivileged userfaultfd Allowed"
canonical: https://openvapt.com/checks/HOST-KRN-028.html
html: https://openvapt.com/checks/HOST-KRN-028.html
site: OpenVAPT, https://openvapt.com/
license: OpenVAPT Source-Available Licence 1.3, https://openvapt.com/legal/licence-text.html
modified: 2026-10-14
version: 0.1.0-alpha.6
---

# HOST-KRN-028 Unprivileged userfaultfd Allowed

Checks that only privileged processes can use userfaultfd.

- Domain: Server
- Severity: Low
- Control category: Secure Configuration
- Fix effort: low
- CVSS v3.1 vector: `CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N`
- CIS Controls v8: 4.1
- NIST CSF 2.0: PR.PS-01
- CWE: CWE-749
- NIST SP 800-53 Rev. 5: AC-6, CM-6
- Benchmark topic: Kernel parameters: vm.unprivileged_userfaultfd (topic only, no benchmark text)

## Why It Matters

userfaultfd lets a process pause the kernel at a chosen moment, which has turned many kernel race conditions into reliable local exploits.

## How It Detects

Reads /proc/sys/vm/unprivileged_userfaultfd directly (no command is run) and compares it with the hardened value 0.

## How to Fix

Create /etc/sysctl.d/60-openvapt-hardening.conf containing:  vm.unprivileged_userfaultfd = 0  then apply with: sysctl --system. Caution: unprivileged live migration tools (for example QEMU post-copy migration or CRIU run as a normal user) need userfaultfd; test those first.

## How to Verify

```
sysctl vm.unprivileged_userfaultfd  should print 0.
```

## Learn the Theory

- [P1 Linux Server Hardening](https://openvapt.com/academy/p1.md)
- [P17 Kernel, Filesystem and Boot Hardening](https://openvapt.com/academy/p17.md)

## References

- [Linux kernel documentation, /proc/sys/vm](https://docs.kernel.org/admin-guide/sysctl/vm.html)

## Source Code

https://github.com/OpenVAPT/openvapt/blob/574f7f3333c44b75a3c649e2d93a76d507f75adf/internal/checks/host/kernel.go

Run it: `openvapt scan --only HOST-KRN-028`. Read it offline: `openvapt explain HOST-KRN-028`.

---

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