CVE-2025-21962

CIFS service interruption via closetimeo conversion overflow

Published Apr 1, 2025 · Updated May 23, 2026

Integer overflow in the Linux CIFS client allows local users to interrupt service through a crafted closetimeo mount option. The closetimeo handler in fs/smb/client/fs_context.c multiplies an untrusted u32 seconds value by HZ before checking its upper limit, allowing the jiffies result to wrap. Reaching the path requires CAP_SYS_ADMIN in the initial user namespace and mounting a CIFS or SMB3 filesystem; the published impact is limited to availability.

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

Integer overflow in the Linux CIFS client allows local users to interrupt service through a crafted closetimeo mount option. The closetimeo handler in fs/smb/client/fs_context.c multiplies an untrusted u32 seconds value by HZ before checking its upper limit, allowing the jiffies result to wrap. Reaching the path requires CAP_SYS_ADMIN in the initial user namespace and mounting a CIFS or SMB3 filesystem; the published impact is limited to availability.

The record

CVE
CVE-2025-21962
Published
Apr 1, 2025
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-190, T1499.004
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 1, 2025CVE publishedPublication date reported by the CVE source.
  2. May 23, 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=1d9cad9c5873097ea141ffc5da1e7921ce765aa8 <513f6cf2e906a504b7ab0b62b2eea993a6f64558
  2. Affected versionversion=5.15.107 <5.15.180
  3. Affected versionversion=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <1c46673be93dd2954f44fe370fb4f2b8e6214224
  4. Affected versionversion=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <6c13fcb7cf59ae65940da1dfea80144e42921e53
  5. Affected versionversion=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <9968fcf02cf6b0f78fbacf3f63e782162603855a
  6. Affected versionversion=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <b24edd5c191c2689c59d0509f0903f9487eb6317
  7. Affected versionversion=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <d5a30fddfe2f2e540f6c43b59cf701809995faef
  8. Affected versionversion=6.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=1d9cad9c5873097ea141ffc5da1e7921ce765aa8 <513f6cf2e906a504b7ab0b62b2eea993a6f64558; version=5.15.107 <5.15.180; version=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <1c46673be93dd2954f44fe370fb4f2b8e6214224; version=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <6c13fcb7cf59ae65940da1dfea80144e42921e53; version=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <9968fcf02cf6b0f78fbacf3f63e782162603855a; version=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <b24edd5c191c2689c59d0509f0903f9487eb6317; version=5efdd9122eff772eae2feae9f0fc0ec02d4846a3 <d5a30fddfe2f2e540f6c43b59cf701809995faef; version=6.0

Published CVSS scores

5.5CISA ADP VulnrichmentCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5CanonicalCVSS: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

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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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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

Technologies

Your stack

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Your stack

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