CVE-2021-22600: Linux Kernel Privilege Escalation Vulnerability

CVE-2021-22600 is a privilege-escalation vulnerability in the Linux kernel’s packet socket (AF_PACKET) implementation. A local user who can reach the flawed code path may trigger incorrect memory freeing, which can crash the system or, in some cases, elevate privileges. Because the kernel underpins nearly every Linux host, unpatched systems remain exposed to local attackers who already have a foothold.

CISA lists the issue and directs organizations to apply vendor updates. Ransomware use is not documented for this CVE. Confirm all version and configuration details against your distribution’s advisory before acting.

How it works

The weakness is classified as CWE-415 (double free). In the AF_PACKET code, memory that has already been released can be freed a second time under certain conditions. A local attacker who can open or manipulate packet sockets may force this double-free condition. The result is either a kernel panic (denial of service) or corruption of kernel memory structures that can be leveraged for privilege escalation. Exact trigger sequences and memory layouts vary by kernel build; do not rely on public proof-of-concept details without validating them against the vendor advisory for your specific kernel.

Am I affected? How to find it in your systems

The vulnerability affects the Linux kernel wherever AF_PACKET support is present—servers, workstations, containers, cloud images, and embedded devices that ship a vulnerable kernel. Inventory steps:

• Enumerate running kernels: uname -r on each host, or query your configuration-management / asset inventory for kernel package versions.
• Identify hosts that expose or use packet sockets (tcpdump, Wireshark, custom packet-capture tools, certain network-monitoring agents, or containers granted CAP_NET_RAW).
• Cross-check the installed kernel package against the security advisory published by your distribution (Red Hat, Ubuntu, SUSE, Debian, cloud-provider kernels, etc.). Only the vendor list is authoritative for fixed versions.
• Review logs for unexpected kernel oops, BUG messages mentioning packet sockets or double-free, or sudden reboots that coincide with local user activity. Telemetry from EDR or kernel crash dumps can surface exploitation attempts, but absence of such signals does not prove safety.

How to remediate

Patch first. Apply the kernel update supplied by your Linux distribution or hardware vendor exactly as described in their advisory for CVE-2021-22600. After installation, reboot into the new kernel and verify the running version. CISA’s required action is simply “Apply updates per vendor instructions.”

Once patched, harden the attack surface that the flaw abused:

• Restrict unprivileged use of AF_PACKET and CAP_NET_RAW via seccomp, capabilities dropping, or Linux Security Modules.
• Run packet-capture tools only in dedicated, least-privilege accounts or containers.
• Keep kernel live-patching solutions current if you rely on them between full reboots.

If you can't patch immediately

Implement compensating controls until the vendor update can be deployed:

• Segment hosts so that untrusted local users cannot reach systems that still run the vulnerable kernel.
• Remove or tightly control CAP_NET_RAW and packet-socket access for non-administrative processes.
• Apply virtual patching or host-based IPS rules that block suspicious AF_PACKET usage patterns if your security tools support them; validate any signature against the vendor advisory.
• Increase monitoring for kernel crashes, unexpected privilege transitions, and anomalous packet-socket activity; forward logs to a central SIEM for correlation.
• Disable unnecessary network-monitoring features that open AF_PACKET sockets until the kernel is updated.

These measures reduce likelihood and impact but do not eliminate the underlying double-free condition.

If your data may have been exposed

Actively exploited local privilege-escalation flaws can be used as a stepping stone after an initial compromise, potentially leading to broader data exposure. If you suspect exploitation, isolate the host, preserve memory and disk images for forensics, and rotate credentials that may have been accessible from the elevated context. You can also run a free exposure scan of your email addresses against known breach data sets to determine whether associated accounts appear in prior incidents.