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CVE-2025-21691 is an incorrect-authorization vulnerability in the Linux kernel cachestat() system call. cachestat(), introduced as a page-cache-statistics interface that avoids mapping files into user virtual address space, omitted the writability-or-ownership permission validation previously added to mincore(). Consequently, cachestat() could expose page-cache statistics for files that the caller neither owns nor can write. The correction adds equivalent permission-checking logic adapted to cachestat() file context.
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No public exploit code observed for this vulnerability.
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9 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Linux kernel cachestat page-cache statistics permission-check flaw.
A Linux kernel information-disclosure/permission-checking flaw in the cachestat() system call. cachestat() did not enforce the conservative writability-or-ownership checks used by mincore(), potentially allowing a locally authenticated, low-privileged user to obtain page-cache statistics for files they should not be able to inspect. The cited Google COS sys-kernel/csql-kernel-6_6 update fixes it in version 19165.0.0 or later.
A Linux kernel cachestat vulnerability involving page cache statistics permission checking, fixed in this Red Hat kernel update.
A Linux kernel vulnerability related to page cache attack techniques; the content indicates it has been remediated by the Linux kernel security team.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.