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

What is CVE-2025-21691?

CVE-2025-21691 is a medium-severity vulnerability in Linux kernel, published on 10 Feb 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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).

Which versions are affected by CVE-2025-21691?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21691?

Apply the vendor's patch.

Is CVE-2025-21691 being exploited?

There is no known exploitation of CVE-2025-21691 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-21691, DEBIAN-CVE-2025-21691, GHSA-3m25-8xh3-c6p2, UBUNTU-CVE-2025-21691.