CVE-2025-21809Network attack vector

System hang via peer-hash lock deadlock

Published Feb 27, 2025 · Updated Aug 5, 2026

Improper locking in Linux allows remote attackers to hang an AFS client through crafted rxrpc traffic on the callback-manager port. rxrpc_new_incoming_peer takes rxnet->peer_hash_lock without disabling bottom halves, while an AFS RCU cleanup can interrupt it and reacquire the same lock. Exploitation requires the kafs module in use and rate-controlled UDP traffic plus address-list churn; the resulting self-deadlock can hard-lock the system.

CVSS severity7.5
High
EPSS probability0.31%
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 allows remote attackers to hang an AFS client through crafted rxrpc traffic on the callback-manager port. rxrpc_new_incoming_peer takes rxnet->peer_hash_lock without disabling bottom halves, while an AFS RCU cleanup can interrupt it and reacquire the same lock. Exploitation requires the kafs module in use and rate-controlled UDP traffic plus address-list churn; the resulting self-deadlock can hard-lock the system.

The record

CVE
CVE-2025-21809
Published
Feb 27, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 27, 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

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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=056fc740be000d39a7dba700a935f3bbfbc664e6
  2. Affected versionversion=6.7.3 <6.8
  3. Affected versionversion=6.8
  4. Affected versionversion=72904d7b9bfbf2dd146254edea93958bc35bbbfe <0e77dd41689637ac4e1b8fe0f27541f373640855
  5. Affected versionversion=72904d7b9bfbf2dd146254edea93958bc35bbbfe <10ba5a3d57af20e494e0d979d1894260989235dd
  6. Affected versionversion=72904d7b9bfbf2dd146254edea93958bc35bbbfe <79d458c13056559d49b5e41fbc4b6890e68cf65b

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=056fc740be000d39a7dba700a935f3bbfbc664e6; version=6.7.3 <6.8; version=6.8; version=72904d7b9bfbf2dd146254edea93958bc35bbbfe <0e77dd41689637ac4e1b8fe0f27541f373640855; version=72904d7b9bfbf2dd146254edea93958bc35bbbfe <10ba5a3d57af20e494e0d979d1894260989235dd; version=72904d7b9bfbf2dd146254edea93958bc35bbbfe <79d458c13056559d49b5e41fbc4b6890e68cf65b

Published CVSS scores

5.5CISA ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
7.5Linux Kernel CNACVSS:3.1/AV:N/AC:L/PR:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
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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