CVE-2025-21681

System lockup via unregistering netdev transmission

Published Jan 31, 2025 · Updated May 23, 2026

Denial of service in Linux kernel Open vSwitch allows local users to lock the system by transmitting to an unregistering netdev. The OVS output path checks carrier state but not whether the device is running, allowing skb_tx_hash to loop forever after real_num_tx_queues reaches zero. Low-privileged local access and transmission during device unregistration are required; recovery from the resulting core lockup requires a reboot.

CVSS severity5.5
Medium
EPSS probability0.22%
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

Denial of service in Linux kernel Open vSwitch allows local users to lock the system by transmitting to an unregistering netdev. The OVS output path checks carrier state but not whether the device is running, allowing skb_tx_hash to loop forever after real_num_tx_queues reaches zero. Low-privileged local access and transmission during device unregistration are required; recovery from the resulting core lockup requires a reboot.

The record

CVE
CVE-2025-21681
Published
Jan 31, 2025
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-835, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 31, 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

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=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <47e55e4b410f7d552e43011baa5be1aab4093990
  2. Affected versionversion=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <82f433e8dd0629e16681edf6039d094b5518d8ed
  3. Affected versionversion=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <ea966b6698785fb9cd0fdb867acd91b222e4723f
  4. Affected versionversion=284be5db6c8d06d247ed056cfc448c4f79bbb16c <87fcf0d137c770e6040ebfdb0abd8e7dd481b504
  5. Affected versionversion=56252da41426f3d01957456f13caf46ce670ea29
  6. Affected versionversion=5efcb301523baacd98a47553d4996e924923114d <930268823f6bccb697aa5d2047aeffd4a497308c
  7. Affected versionversion=6.1.25 <6.1.127
  8. Affected versionversion=6.2.12 <6.3
  9. Affected versionversion=6.3
  10. Affected versionversion=644b3051b06ba465bc7401bfae9b14963cbc8c1c <ea9e990356b7bee95440ba0e6e83cc4d701afaca
  11. Affected versionversion=9b0dd09c1ceb35950d2884848099fccc9ec9a123 <b5c73fc92f8d15c16e5dc87b5c17d2abf1e6d092

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <47e55e4b410f7d552e43011baa5be1aab4093990; version=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <82f433e8dd0629e16681edf6039d094b5518d8ed; version=066b86787fa3d97b7aefb5ac0a99a22dad2d15f8 <ea966b6698785fb9cd0fdb867acd91b222e4723f; version=284be5db6c8d06d247ed056cfc448c4f79bbb16c <87fcf0d137c770e6040ebfdb0abd8e7dd481b504; version=56252da41426f3d01957456f13caf46ce670ea29; version=5efcb301523baacd98a47553d4996e924923114d <930268823f6bccb697aa5d2047aeffd4a497308c; version=6.1.25 <6.1.127; version=6.2.12 <6.3; version=6.3; version=644b3051b06ba465bc7401bfae9b14963cbc8c1c <ea9e990356b7bee95440ba0e6e83cc4d701afaca; version=9b0dd09c1ceb35950d2884848099fccc9ec9a123 <b5c73fc92f8d15c16e5dc87b5c17d2abf1e6d092

Published CVSS scores

5.5NISTCVSS: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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
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

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