CVE-2021-4442Public exploit

Kernel warning via nonempty repair queue resequencing

Published Aug 29, 2024 · Updated May 11, 2026

Improper state validation in the Linux kernel allows local users to trigger a TCP receive-path warning through TCP repair options. The TCP_QUEUE_SEQ handler accepts a new receive or transmit sequence number after data has been restored, although sequence changes are valid only while the selected queue is empty. Reachability requires privileged local access to TCP repair mode; the demonstrated consequences are inconsistent socket state, a kernel warning, and connection reset.

CVSS severityUnavailable
Unscored
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper state validation in the Linux kernel allows local users to trigger a TCP receive-path warning through TCP repair options. The TCP_QUEUE_SEQ handler accepts a new receive or transmit sequence number after data has been restored, although sequence changes are valid only while the selected queue is empty. Reachability requires privileged local access to TCP repair mode; the demonstrated consequences are inconsistent socket state, a kernel warning, and connection reset.

The record

CVE
CVE-2021-4442
Published
Aug 29, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Aug 29, 2024CVE 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=3.5
  2. Affected versionversion=ee9952831cfd0bbe834f4a26489d7dce74582e37 <046f3c1c2ff450fb7ae53650e9a95e0074a61f3e
  3. Affected versionversion=ee9952831cfd0bbe834f4a26489d7dce74582e37 <319f460237fc2965a80aa9a055044e1da7b3692a
  4. Affected versionversion=ee9952831cfd0bbe834f4a26489d7dce74582e37 <3b72d5a703842f582502d97906f17d6ee122dac2
  5. Affected versionversion=ee9952831cfd0bbe834f4a26489d7dce74582e37 <3bf899438c123c444f6b644a57784dfbb6b15ad6
  6. Affected versionversion=ee9952831cfd0bbe834f4a26489d7dce74582e37 <8811f4a9836e31c14ecdf79d9f3cb7c5d463265d

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=3.5; version=ee9952831cfd0bbe834f4a26489d7dce74582e37 <046f3c1c2ff450fb7ae53650e9a95e0074a61f3e; version=ee9952831cfd0bbe834f4a26489d7dce74582e37 <319f460237fc2965a80aa9a055044e1da7b3692a; version=ee9952831cfd0bbe834f4a26489d7dce74582e37 <3b72d5a703842f582502d97906f17d6ee122dac2; version=ee9952831cfd0bbe834f4a26489d7dce74582e37 <3bf899438c123c444f6b644a57784dfbb6b15ad6; version=ee9952831cfd0bbe834f4a26489d7dce74582e37 <8811f4a9836e31c14ecdf79d9f3cb7c5d463265d

Published CVSS scores

No CVSS assessment is available in this record.

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

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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