CVE-2021-28699 : Exploit Details and Defense Strategies

CVE-2021-28699, also known as inadequate grant-v2 status frames array bounds check, is a security vulnerability affecting Xen containers. This article provides insights into the nature of the vulnerability, its impact, and mitigation strategies.

Understanding CVE-2021-28699

CVE-2021-28699 is a security vulnerability in Xen containers that can potentially lead to Denial of Service (DoS) attacks, privilege escalation, and information leaks.

What is CVE-2021-28699?

The vulnerability arises from an inadequate bounds check for grant-v2 status frames in Xen containers. Malicious or buggy guest kernels could exploit this vulnerability to launch DoS attacks and affect the entire system.

The Impact of CVE-2021-28699

Malicious actors could leverage this vulnerability to disrupt system operations through DoS attacks. Furthermore, there is a risk of privilege escalation and potential information leakage, posing a significant threat to system security.

Technical Details of CVE-2021-28699

The vulnerability originates in the v2 grant table interface of Xen containers. When operating in this mode, a guest has two tables, and guests need to retrieve the addresses for accessing the new status tracking table.

Vulnerability Description

The translation of frame numbers of the grant status table involves an inadequate bounds check, potentially leading to array overflows and unauthorized access to system memory.

Affected Systems and Versions

Xen versions from 4.10 onwards are susceptible to this vulnerability. Only 32-bit x86 guests using grant table version 2 interfaces are impacted.

Exploitation Mechanism

Malicious or buggy guest kernels may exploit this vulnerability to mount DoS attacks affecting the entire system, with the possibility of privilege escalation and information leaks.

Mitigation and Prevention

Addressing CVE-2021-28699 requires immediate actions to secure Xen containers and prevent potential exploits.

Immediate Steps to Take

To mitigate the risk, avoid increasing the number of grant table frames beyond the specified limits. Additionally, consider suppressing the use of grant table v2 interfaces for 32-bit x86 guests.

Long-Term Security Practices

Implement regular security updates and patches for Xen containers to address known vulnerabilities and enhance system resilience against potential threats.

Patching and Updates

Stay informed about security advisories and releases from Xen to apply relevant patches promptly and maintain a secure container environment.