CVE-2025-21654

Fanotify identifier loss via premature alias lookup

Published Jan 19, 2025 · Updated May 11, 2026

File-handle encoding failure in Linux allows local users to trigger a kernel warning and omit identifiers from OverlayFS deletion events. The ovl_encode_fh() path looks up a dentry alias before determining whether a non-decodable file handle needs one, so a watched inode whose aliases were discarded cannot be encoded. Reaching the condition requires an OverlayFS watch and discarded dentry aliases; the result is a warning and missing FAN_DELETE_SELF file identifiers.

CVSS severity5.5
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

File-handle encoding failure in Linux allows local users to trigger a kernel warning and omit identifiers from OverlayFS deletion events. The ovl_encode_fh() path looks up a dentry alias before determining whether a non-decodable file handle needs one, so a watched inode whose aliases were discarded cannot be encoded. Reaching the condition requires an OverlayFS watch and discarded dentry aliases; the result is a warning and missing FAN_DELETE_SELF file identifiers.

The record

CVE
CVE-2025-21654
Published
Jan 19, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 19, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <3c7c90274ae339e1ad443c9be1c67a20b80b9c76
  2. Affected versionversion=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <c45beebfde34aa71afbc48b2c54cdda623515037
  3. Affected versionversion=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <f0c0ac84de17c37e6e84da65fb920f91dada55ad
  4. Affected versionversion=6.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <3c7c90274ae339e1ad443c9be1c67a20b80b9c76; version=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <c45beebfde34aa71afbc48b2c54cdda623515037; version=16aac5ad1fa94894b798dd522c5c3a6a0628d7f0 <f0c0ac84de17c37e6e84da65fb920f91dada55ad; version=6.6

Published CVSS scores

5.5UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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