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CVE Record

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

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).

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2025-21691 is a Linux kernel permission-checking flaw in the cachestat system call. It could let a local caller obtain page-cache statistics where prior Linux hardening intended ownership or writability checks. The sources do not provide CVSS, impact details, or active exploitation evidence.

Executive priority

Treat as a routine-to-priority kernel patching item for shared Linux environments. It does not have confirmed active exploitation in the provided sources, but kernel permission flaws deserve timely remediation because local access boundaries often matter in hosted and multi-tenant systems.

Technical view

The cachestat syscall, introduced as a faster mincore-like interface, missed the conservative permission logic previously added to mincore. The kernel fix adds equivalent ownership or writability checks adapted to file context. Listed affected Linux versions include 6.5 and later stable ranges before referenced fixes.

Likely exposure

Exposure is most relevant on Linux systems running affected kernels where untrusted local users, hosted workloads, or containers can invoke kernel syscalls. Distribution backports may change apparent version exposure, so package advisory status matters more than upstream version alone.

Exploitation context

The bundle marks KEV as false and cites no active exploitation. The described issue appears local and permission-related, concerning visibility into page-cache statistics rather than remote code execution. Exploitability and practical impact are not fully detailed in the provided sources.

Researcher notes

Focus review on cachestat permission checks versus mincore’s conservative ownership or writability model. The public bundle confirms the missing logic and stable kernel fixes, but does not include CVSS, CWE, detailed exploit primitives, or distribution-specific affected package data.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Check your distribution advisory for CVE-2025-21691 backport status.
  • Prioritize multi-user, shared hosting, and container-dense Linux systems.
  • Reboot into the patched kernel after maintenance.
  • Track vendor guidance if upstream version mapping is unclear.

Validation and detection

  • Inventory running Linux kernel versions across affected assets.
  • Confirm vendor packages include a CVE-2025-21691 fix or equivalent backport.
  • Verify patched systems are booted into the updated kernel.
  • Review exposure of systems allowing untrusted local code execution.
  • Document any unsupported kernels needing upgrade or isolation.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2025-21691 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
5Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxcf264e1329fb0307e044f7675849f9f38b44c11a, cf264e1329fb0307e044f7675849f9f38b44c11a, cf264e1329fb0307e044f7675849f9f38b44c11a, cf264e1329fb0307e044f7675849f9f38b44c11aunaffected
LinuxLinux6.5, 0, 6.6.75, 6.12.12, 6.13.1, 6.14affected
Weakness

CWE details

No CWE listed

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