KubeArmor vs CVE-2021-4034

In this session of AccuKnox Office Hours, the demo was given by Harshit Anand and Tamilmaran, security engineers. We will learn about the Polkit vulnerability, what’s it about and how one can defend it using KubeArmor, an AccuKnox open-source.

Defending Against CVE-2021-4034 Polkit with AccuKnox

In early 2022, a severe vulnerability shook the Linux ecosystem: CVE-2021-4034, commonly known as Polkit or PwnKit. This long-standing flaw, present for over a decade, allows any unprivileged local user to escalate privileges to root on vulnerable systems. The vulnerability resides in Polkit’s pkexec utility, which is widely available across major Linux distributions such as Ubuntu, CentOS, Debian, and more. In this post, we’ll explore the nature of CVE-2021-4034 Polkit, its implications for enterprise security, and how AccuKnox’s KubeArmor can help defend against such exploits—even before a patch is applied.

What Is CVE-2021-4034 Polkit?

Polkit (PolicyKit) is a component used in Unix-like operating systems to control system-wide privileges. It allows non-privileged processes to communicate with privileged ones in a secure manner. The vulnerability lies in the pkexec binary, which is designed to execute commands with elevated privileges. Due to a memory corruption flaw in how pkexec processes command-line arguments, attackers can manipulate environment variables like LD_PRELOAD to inject malicious shared libraries and gain root access.

What makes this vulnerability so dangerous is that the vulnerable binary is pre-installed in most Linux systems—no additional malware or tools are needed. An attacker with local access can simply run a script exploiting this flaw and instantly gain full control over the system.

Real-World Threats to Cloud Workloads

For cloud-native environments running Kubernetes, this vulnerability poses a serious risk. Exploiting CVE-2021-4034 Polkit inside a container could allow attackers to escape the container context and compromise the host system or other workloads. Although patches were released shortly after the vulnerability became public, many systems remain unpatched, especially in large enterprise deployments where updates take time to roll out.

In a live demo during AccuKnox’s office hours, security engineers demonstrated how easily this vulnerability can be exploited in a Kubernetes pod running an unpatched Ubuntu image. By compiling and running a simple C exploit, they were able to gain root shell access within seconds—highlighting the urgency of runtime protection.

Defending with AccuKnox and KubeArmor

AccuKnox offers a powerful, Kubernetes-native solution called KubeArmor that provides zero trust runtime security. Unlike traditional antivirus or signature-based tools, KubeArmor enforces granular security policies at the system level. It can block unauthorized access to specific files, binaries, and processes—even unknown zero-day exploits.

To mitigate CVE-2021-4034 Polkit, AccuKnox recommends applying a security policy that explicitly denies execution of the vulnerable pkexec binary inside containers or virtual machines. In the demo, after applying such a policy through KubeArmor, attempts to exploit the vulnerability were effectively blocked. The exploit script failed to gain root access, and KubeArmor generated detailed audit logs showing the denied action.

Why Choose KubeArmor?

• Policy-Driven Security: KubeArmor uses policy-as-code to define allowed behaviors, making it easy to integrate into CI/CD pipelines.
  
• Real-Time Enforcement: Policies are enforced at runtime, allowing protection before patches are deployed.
  
• Zero-Day Mitigation: Even unknown vulnerabilities can be mitigated by restricting suspicious or privileged operations.
  
• Audit and Compliance: KubeArmor logs all denied actions, providing valuable forensic insights and ensuring compliance with industry standards.
  

Conclusion

The discovery of CVE-2021-4034 Polkit is a stark reminder of how legacy components can introduce critical security risks—even in modern cloud environments. While patching remains essential, relying solely on reactive measures is no longer sufficient.

With AccuKnox and KubeArmor, organizations can enforce zero trust runtime security policies that prevent exploits like PwnKit from causing harm—regardless of whether a vulnerability is known or has yet to be discovered. It’s time to shift from reactive patching to proactive protection.To learn more about securing your workloads with AccuKnox, visit accunox.com or explore KubeArmor on GitHub.

Now you can protect your workloads in minutes using AccuKnox, it is available to protect your Kubernetes and other cloud workloads using Kernel Native Primitives such as AppArmor, SELinux, and eBPF.

Let us know if you are seeking additional guidance in planning your cloud security program.

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