CVE-2021-29650

Kernel panic via incomplete x_tables memory barriers

Published Mar 30, 2021 · Updated Aug 3, 2024

Race condition in Linux kernel netfilter before 5.11.11 allows local users to cause a system crash by repeatedly replacing x_tables rules. xt_replace_table and xt_write_recseq_begin use write-only barriers where sequence-counter reads require full memory barriers, allowing stale ordering during table replacement. Local access with permission to replace netfilter tables is required; successful triggering panics the kernel and interrupts the host.

CVSS severity5.5
Medium
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in Linux kernel netfilter before 5.11.11 allows local users to cause a system crash by repeatedly replacing x_tables rules. xt_replace_table and xt_write_recseq_begin use write-only barriers where sequence-counter reads require full memory barriers, allowing stale ordering during table replacement. Local access with permission to replace netfilter tables is required; successful triggering panics the kernel and interrupts the host.

The record

CVE
CVE-2021-29650
Published
Mar 30, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C

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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