CISA KEV · Known exploitedHigh

CVE-2021-22555

Linux Kernel

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

CVSS
7.8
EPSS
78.7%
99.5% percentile
CISA KEV
Listed
Published
2021.07.07
PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV
Exploit probability78.7%
Technical severityCVSS 7.8

Vulnerability overview

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

Affected product and versions

Product
Linux Kernel
Affected versions
2.6.19-rc1, >= 2.6.19 < 4.4.267, >= 4.5 < 4.9.267, >= 4.10 < 4.14.231, >= 4.15 < 4.19.188, >= 4.20 < 5.4.113, >= 5.5 < 5.10.31, >= 5.11 < 5.12
Fixed versions
4.4.267, 4.9.267, 4.14.231, 4.19.188, 5.4.113, 5.10.31, 5.12

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
CISA required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Due date: 2025.10.27
  1. 1
    Identify

    Confirm that Linux Kernel and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-787
KEV added
2025.10.06
Ransomware use
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