CVE-2025-21736

Local service interruption via shifted block count

Published Feb 27, 2025 · Updated May 11, 2026

Integer overflow in Linux kernel NILFS2 before fixed stable releases allows local users to interrupt service through a fiemap request. In fs/nilfs2/inode.c, nilfs_fiemap() left-shifts a potentially INT_MAX block count by blkbits in a narrower integer, allowing n to overflow. A local low-privileged user must reach fiemap on a NILFS2 file; published scoring limits the reported effect to availability.

CVSS severity5.5
Medium
EPSS probability0.25%
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 Linux kernel NILFS2 before fixed stable releases allows local users to interrupt service through a fiemap request. In fs/nilfs2/inode.c, nilfs_fiemap() left-shifts a potentially INT_MAX block count by blkbits in a narrower integer, allowing n to overflow. A local low-privileged user must reach fiemap on a NILFS2 file; published scoring limits the reported effect to availability.

The record

CVE
CVE-2025-21736
Published
Feb 27, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 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=2.6.38
  2. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <250423300b4b0335918be187ef3cade248c06e6a
  3. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <58b1c6881081f5ddfb9a14dc241a74732c0f855c
  4. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <6438ef381c183444f7f9d1de18f22661cba1e946
  5. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <7649937987fed51ed09985da4019d50189fc534e
  6. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <8f41df5fd4c11d26e929a85f7239799641f92da7
  7. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <b9495a9109abc31d3170f7aad7d48aa64610a1a2
  8. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <f2bd0f1ab47822fe5bd699c8458b896c4b2edea1
  9. Affected versionversion=622daaff0a8975fb5c5b95f24f3234550ba32e92 <f3d80f34f58445355fa27b9579a449fb186aa64e

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2.6.38; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <250423300b4b0335918be187ef3cade248c06e6a; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <58b1c6881081f5ddfb9a14dc241a74732c0f855c; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <6438ef381c183444f7f9d1de18f22661cba1e946; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <7649937987fed51ed09985da4019d50189fc534e; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <8f41df5fd4c11d26e929a85f7239799641f92da7; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <b9495a9109abc31d3170f7aad7d48aa64610a1a2; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <f2bd0f1ab47822fe5bd699c8458b896c4b2edea1; version=622daaff0a8975fb5c5b95f24f3234550ba32e92 <f3d80f34f58445355fa27b9579a449fb186aa64e

Published CVSS scores

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

T1499Endpoint Denial of Service

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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