CVE-2025-21817

System hang via reclaim deadlock in sysfs store

Published Feb 27, 2025 · Updated Sep 7, 2026

Improper locking in Linux 6.12.96 through 6.12.108 and 6.13.2 allows local users to hang the system via a block-device sysfs store. While a block request queue is frozen, update_nr_requests, wbt, and scheduler store callbacks allocate with GFP_KERNEL, allowing direct reclaim to reenter I/O and deadlock. Local access and permission to write the affected block-queue sysfs attributes are required; a successful trigger can stall kernel I/O and hang the host.

CVSS severity5.5
Medium
EPSS probability0.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper locking in Linux 6.12.96 through 6.12.108 and 6.13.2 allows local users to hang the system via a block-device sysfs store. While a block request queue is frozen, update_nr_requests, wbt, and scheduler store callbacks allocate with GFP_KERNEL, allowing direct reclaim to reenter I/O and deadlock. Local access and permission to write the affected block-queue sysfs attributes are required; a successful trigger can stall kernel I/O and hang the host.

The record

CVE
CVE-2025-21817
Published
Feb 27, 2025
Updated
Sep 7, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 7, 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=1645cd7fd42c236c952e9228badcac4fea1829ea <a09280c39ea54080daf19cfaf4a3121a8d17d5cd
  2. Affected versionversion=6.12.96 <6.12.109
  3. Affected versionversion=6.13.2 <6.13.3
  4. Affected versionversion=8985da5481562e96b95e94ed8e5cc9b6565eb82b <2566ce907e5d5db8a039647208e029ce559baa31
  5. Affected versionversion=c99f66e4084a62a2cc401c4704a84328aeddc9ec <7c0be4ead1f8f5f8be0803f347de0de81e3b8e1c

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

The Linux Kernel Organization · Linuxversion=1645cd7fd42c236c952e9228badcac4fea1829ea <a09280c39ea54080daf19cfaf4a3121a8d17d5cd; version=6.12.96 <6.12.109; version=6.13.2 <6.13.3; version=8985da5481562e96b95e94ed8e5cc9b6565eb82b <2566ce907e5d5db8a039647208e029ce559baa31; version=c99f66e4084a62a2cc401c4704a84328aeddc9ec <7c0be4ead1f8f5f8be0803f347de0de81e3b8e1c

Published CVSS scores

5.5NIST NVDCVSS: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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
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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