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Actively exploited · Published Jul 7, 2021 · Assigned by Google

CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE

High 8.3 Exploited

In plain English

A high-severity out-of-bounds write in Linux Kernel. Attackers are actively exploiting it in the wild (listed by CISA on October 6, 2025). The chance it is exploited in the next 30 days is estimated at 78.7% (higher than 99.6% of all known vulnerabilities). Ready-made attack tooling exists: Metasploit, public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.3High
Exploit odds (30 days)78.7%top 0.4% of all CVEs
Exploited in the wildYesCISA KEV since Oct 6, 2025
Attack tooling2Metasploit, Public PoC

CISA guidance

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

Federal agencies must remediate by Oct 27, 2025.

Official description

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 packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:8kernel-tools-libs-devel4.18.0-305.12.1.el8_4ALSA-2021:3057
Debian:12linux5.10.38-1DEBIAN-CVE-2021-22555
Debian:13linux5.10.38-1DEBIAN-CVE-2021-22555
Debian:14linux5.10.38-1DEBIAN-CVE-2021-22555
Rocky Linux:8kernel0:4.18.0-305.12.1.el8_4RLSA-2021:3057
Rocky Linux:8kernel-rt0:4.18.0-305.12.1.rt7.84.el8_4RLSA-2021:3088
Ubuntu:22.04:LTSlinux-intel-iot-realtimeno fix listedUBUNTU-CVE-2021-22555
Ubuntu:24.04:LTSlinux-raspi-realtimeno fix listedUBUNTU-CVE-2021-22555
Ubuntu:22.04:LTSlinux-realtimeno fix listedUBUNTU-CVE-2021-22555

Affected products (as reported)

VendorProductVersions
n/a Linux Kernel 2.6.19-rc1 – before unspecified

Weakness: CWE-787 · Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

References