CVE-2025-21691 [Medium] | Security Vulnerability in Linux Kernel

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).

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.04%	0.19%	+0.15%
2	2025-11-20	0.07%	0.04%	-0.03%
3	2025-11-18	—	0.07%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.04%

0.19%

+0.15%

2025-11-20

0.07%

0.04%

-0.03%

2025-11-18

—

0.07%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	3.6	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

3.6

[email protected]

OS Trackers for CVE-2025-21691

vendor	priority	summary	link
`debian`	unimportant	CVE-2025-21691 unimportant priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2025-21691
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2025-21691
`suse`	medium	CVE-2025-21691 severity moderate: SUSE including 52 source package names (cluster-md-kmp-default, dlm-kmp-default, …), 271 product×package rows across 47 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Linux Enterprise High Availability Extension 12 SP5, … (47 product lines)): Known Not Affected 245, Fixed 26.	https://www.suse.com/security/cve/CVE-2025-21691/
`ubuntu`	medium	CVE-2025-21691 medium priority: Ubuntu including 150 source packages (linux, linux-allwinner-5.19, …), 1487 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1097, ignored 148, released 128, not-affected 114.	https://ubuntu.com/security/CVE-2025-21691

Affected software / configurations for CVE-2025-21691

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 6.5, < 6.6.75	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.7, < 6.12.12	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	6.13	cpe:2.3:o:linux:linux_kernel:6.13:::::::*

References for CVE-2025-21691

URL	Tags
https://git.kernel.org/stable/c/5f537664e705b0bf8b7e329861f20128534f6a83	Patch
https://git.kernel.org/stable/c/780ab8329672464984cf1344bd5c3993af0226c7	Patch
https://git.kernel.org/stable/c/7d6405c13b0d8a8367cd8df63f118b619a3f0dd2	Patch
https://git.kernel.org/stable/c/97153a05077f618f7471f50a78158602badccb30	Patch

URL

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

Exploit prediction scoring system (EPSS) score for CVE-2025-21691

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21691

Weakness enumeration for CVE-2025-21691

OS Trackers for CVE-2025-21691

Affected software / configurations for CVE-2025-21691

References for CVE-2025-21691