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CVE-2021-22555

High CVSS 8.3 Known exploited

Published 2021-07-07 · last changed 2026-06-17 · added to CISA KEV 2025-10-06

This one is being exploited in the wild.

CISA added CVE-2021-22555 to the Known Exploited Vulnerabilities catalog on 2025-10-06. Federal agencies are required to remediate it on a deadline. If you have affected machines, this is the class of finding that moves ahead of the rest of the queue.

The fix

We hold no Microsoft remediation data for CVE-2021-22555, which normally means it is not a Windows CVE. For non-Microsoft software the fix is the vendor's own updated release, and the affected versions are listed below.

What it is

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

Sources

CVSS vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H