CVE-2021-22555Known exploitationPublic exploit

Privilege escalation via netfilter compatibility padding overwrite

Published Jul 7, 2021 · Updated Dec 30, 2025

Heap out-of-bounds write in affected Linux Kernel releases allows local users to gain kernel privileges or crash the system. In xt_compat_target_from_user(), an allocation omits target->targetsize, so a padding memset writes zeros beyond the converted ruleset blob. Reachability requires a 32-bit compatibility setsockopt path and CAP_NET_ADMIN, which an unprivileged local user obtains only when user and network namespaces are enabled.

CVSS severity8.3
High
EPSS probability78.68%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap out-of-bounds write in affected Linux Kernel releases allows local users to gain kernel privileges or crash the system. In xt_compat_target_from_user(), an allocation omits target->targetsize, so a padding memset writes zeros beyond the converted ruleset blob. Reachability requires a 32-bit compatibility setsockopt path and CAP_NET_ADMIN, which an unprivileged local user obtains only when user and network namespaces are enabled.

The record

CVE
CVE-2021-22555
Published
Jul 7, 2021
Updated
Dec 30, 2025
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-787, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 30, 2025Record 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=2.6.19-rc1 <unspecified

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=2.6.19-rc1 <unspecified

Published CVSS scores

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
7.8Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.3Google LLCCVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/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)
Vectorlocal
Privilegesauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1068Exploitation for Privilege Escalation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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