Actively exploited

CVE-2021-22600 Linux Kernel Privilege Escalation Vulnerability

Linux Kernel contains a flaw in the packet socket (AF_PACKET) implementation which could lead to incorrectly freeing memory. A local user could exploit this for denial-of-service (DoS) or possibly for privilege escalation.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch urgentlyCybergen assessment

CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 11 Apr 2022.
Rated Medium severity (CVSS 6.6, scored by Vendor).
It has been in the catalogue for 1,670 days. Systems still unpatched now have almost certainly been scanned for it.

The Vulnerability

What It Is

A double free bug in packet_set_ring() in net/packet/af_packet.c can be exploited by a local user through crafted syscalls to escalate privileges or deny service. We recommend upgrading kernel past the effected versions or rebuilding past ec6af094ea28f0f2dda1a6a33b14cd57e36a9755

Affected Versions

Product	Versions
Linux Kernel Kernel	unspecified to before 5.4.168 unspecified to before 5.10.88 unspecified to before 5.15.11 unspecified to before 5.16-rc6

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

1
Find it
Search your asset inventory and external attack surface for Linux Kernel. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management
2
Fix it
Apply updates per vendor instructions.
Vulnerability Management
3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response
4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing

Vendor Advisories

nvd.nist.gov/vuln/detail/CVE-2021-22600

Regulation

The Compliance Clock

Cyber EssentialsCyber Essentials requires high and critical updates (CVSS 7.0 or above) within 14 days of release. Treat any exploited flaw the same way.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 2 May 2022 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

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More Exploited Linux Flaws

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CVE-2021-22600 Linux Kernel Privilege Escalation Vulnerability

Should You Worry?

What It Is

Affected Versions

What To Do Now

Find it

Fix it

Hunt for compromise

Prove it is fixed

Vendor Advisories

The Compliance Clock

More Exploited Linux Flaws

Not Sure If You Are Exposed?

Sources