CVE-2025-21646Public exploit

Kernel warning via oversized AFS cell name

Published Jan 19, 2025 · Updated Aug 5, 2026

Improper input validation in the Linux kernel AFS filesystem allows local users to trigger a kernel warning via a 256-byte cell name. AFS accepts that name and passes it to procfs as a directory name even though procfs permits only 255-byte filenames. Reaching the path requires local low-privileged access to an AFS-enabled kernel; the demonstrated consequence is the warning.

CVSS severity5.5
Medium
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Improper input validation in the Linux kernel AFS filesystem allows local users to trigger a kernel warning via a 256-byte cell name. AFS accepts that name and passes it to procfs as a directory name even though procfs permits only 255-byte filenames. Reaching the path requires local low-privileged access to an AFS-enabled kernel; the demonstrated consequence is the warning.

The record

CVE
CVE-2025-21646
Published
Jan 19, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 19, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=5.8
  2. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7673030efe0f8ca1056d3849d61784c6caa052af
  3. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7922b1f058fe24a93730511dd0ae2e1630920096
  4. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7cb3e77e9b4e6ffa325a5559393d3283c9af3d01
  5. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8
  6. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <9340385468d056bb700b8f28df236b81fc86a079
  7. Affected versionversion=c3e9f888263bb4df11cbd623ceced02081cb2f9f <aabe47cf5ac5e1db2ae0635f189d836f67024904

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.8; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7673030efe0f8ca1056d3849d61784c6caa052af; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7922b1f058fe24a93730511dd0ae2e1630920096; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <7cb3e77e9b4e6ffa325a5559393d3283c9af3d01; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <9340385468d056bb700b8f28df236b81fc86a079; version=c3e9f888263bb4df11cbd623ceced02081cb2f9f <aabe47cf5ac5e1db2ae0635f189d836f67024904

Published CVSS scores

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

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo