CVE-2021-4440 Vulnerability Analysis: Impact, Mitigation, and Security Recommendations

Executive Summary

CVE-2021-4440 is a critical vulnerability identified in the Linux Kernel, specifically affecting the x86/xen subsystem. This vulnerability, involving the

USERGS_SYSRET64

paravirt call, has the potential to allow arbitrary code execution or cause a denial of service (DoS). The vulnerability has been addressed by removing this call in the affected versions. Although there have been no confirmed reports of this vulnerability being exploited in the wild, it is imperative for organizations to take immediate action to patch and update their systems to mitigate potential risks.

Technical Information

CVE-2021-4440 is a critical security flaw in the Linux Kernel's x86/xen subsystem. The vulnerability is rooted in the

USERGS_SYSRET64

paravirt call, which is used for handling system returns in a paravirtualized environment. The improper handling of this call can lead to severe consequences, including arbitrary code execution or a denial of service (DoS).

The vulnerability affects Linux Kernel versions up to 5.10.217. The severity of this vulnerability is classified as critical due to the potential impact on system security and stability. The issue arises from the way the

USERGS_SYSRET64

paravirt call is managed, which could be exploited by an attacker to execute arbitrary code or disrupt system operations.

The technical details of the vulnerability are as follows: the

USERGS_SYSRET64

paravirt call is designed to handle system returns in a paravirtualized environment. However, due to improper handling, this call can be manipulated to execute arbitrary code or cause a denial of service. The vulnerability has been addressed by removing the

USERGS_SYSRET64

paravirt call in the affected versions of the Linux Kernel.

Exploitation in the Wild

As of now, there have been no confirmed reports of CVE-2021-4440 being exploited in the wild. The CVE Exploit in the Wild Finder tool indicates that there are no reports of this vulnerability being actively targeted by threat actors. This suggests that, while the vulnerability is critical, it has not yet been exploited by malicious actors. However, the absence of exploitation reports does not diminish the importance of addressing this vulnerability promptly.

APT Groups using this vulnerability

There are no specific Advanced Persistent Threat (APT) groups known to exploit CVE-2021-4440 as of the latest information available. The CVE Threat Actors Finder tool returned no results, indicating that no known APT groups have been identified as exploiting this vulnerability. It is crucial for organizations to remain vigilant and monitor for any emerging threats related to this vulnerability.

Affected Product Versions

The vulnerability affects the Linux Kernel up to version 5.10.217. It is essential for organizations using affected versions of the Linux Kernel to update to a patched version to mitigate the risks associated with CVE-2021-4440. The following versions are affected:

Linux Kernel versions up to 5.10.217

Workaround and Mitigation

The primary mitigation strategy for CVE-2021-4440 is to update the Linux Kernel to a version where the

USERGS_SYSRET64

paravirt call has been removed. This fix is available in versions post 5.10.217. Organizations should follow the specific guidance provided by their Linux distribution vendor to ensure that their systems are protected.

For example, Red Hat and Amazon Linux have released advisories and patches for this vulnerability. It is recommended to apply these patches as soon as possible to mitigate the risks associated with CVE-2021-4440. Additionally, organizations should continuously monitor their systems for any signs of exploitation and adhere to best practices for system security.

References

NVD - CVE-2021-4440: https://nvd.nist.gov/vuln/detail/CVE-2021-4440

grsecurity - CVE-2021-4440: A Linux CNA Case Study: https://grsecurity.net/cve-2021-4440_linux_cna_case_study

Amazon Linux Security Center - CVE-2021-4440: https://explore.alas.aws.amazon.com/CVE-2021-4440.html

Red Hat Bugzilla - CVE-2021-4440: https://bugzilla.redhat.com/show_bug.cgi?id=2294289

VulDB - CVE-2021-4440: https://vuldb.com/?id.269634

Rescana is here for you

At Rescana, we understand the critical importance of staying ahead of cybersecurity threats. Our Continuous Threat and Exposure Management (CTEM) platform is designed to help you identify, assess, and mitigate vulnerabilities in your systems. We are committed to providing you with the tools and insights needed to protect your organization from potential threats. If you have any questions about this report or any other issue, please do not hesitate to contact us at ops@rescana.com.