CVE-2021-22042: VMware Cloud Foundation Auth Bypass Flaw

CVE-2021-22042 Overview

CVE-2021-22042 is an unauthorized access vulnerability affecting VMware ESXi that stems from the VMX process having improper access to settingsd authorization tickets. This vulnerability allows a malicious actor with privileges within the VMX process to access the settingsd service, which runs with elevated privileges. Successful exploitation could enable attackers to escalate their privileges on affected ESXi hosts, potentially compromising the integrity and confidentiality of the virtualization infrastructure.

Critical Impact
An attacker with VMX process access can escalate privileges to access the high-privileged settingsd service, potentially compromising VMware ESXi hosts and VMware Cloud Foundation deployments.

Affected Products

VMware ESXi 7.0 Update 1
VMware ESXi 7.0 Update 2
VMware ESXi 7.0 Update 3
VMware Cloud Foundation (multiple versions)

Discovery Timeline

2022-02-16 - CVE-2021-22042 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-22042

Vulnerability Analysis

This vulnerability is classified as CWE-863 (Incorrect Authorization), indicating a fundamental flaw in how access controls are implemented within the VMware ESXi architecture. The core issue lies in the relationship between the VMX process (Virtual Machine eXecutable) and the settingsd service.

In VMware ESXi, the VMX process is responsible for managing individual virtual machines and their hardware emulation. The settingsd service operates with elevated privileges and handles various system configuration tasks. Under normal circumstances, the VMX process should not have access to settingsd authorization tickets.

The vulnerability allows an attacker who has already gained code execution within the VMX process context to leverage improperly accessible authorization tickets. This creates a privilege escalation pathway from a VM-scoped process to a system-level service, effectively breaking the security boundary between virtual machine management and host system administration.

Root Cause

The root cause of CVE-2021-22042 is an incorrect authorization implementation where VMX processes are granted or can obtain access to settingsd authorization tickets that should be restricted. This represents a failure in the principle of least privilege, where the VMX process has more access than required for its intended functionality. The authorization mechanism fails to properly validate or restrict which processes can use settingsd tickets, creating an unintended privilege escalation vector.

Attack Vector

The attack vector for this vulnerability is local, requiring an attacker to first establish a foothold within the VMX process. This could occur through:

VM Escape: An attacker who successfully escapes from a guest VM into the VMX process could leverage this vulnerability for further privilege escalation
Compromised VM Configuration: Exploiting other vulnerabilities in VM handling that grant VMX process access
Malicious Administrator Access: An attacker with limited administrative access to virtual machine management could exploit the improper authorization to access higher-privileged services

Once within the VMX process context, the attacker can access the settingsd authorization tickets and authenticate to the settingsd service as if they were a high-privileged user. This lateral movement from VMX to settingsd represents a significant privilege escalation within the ESXi host.

The vulnerability mechanism involves improper access control between the VMX process and the settingsd service. When exploited, an attacker within the VMX process can obtain and use settingsd authorization tickets to authenticate with elevated privileges. For complete technical details, refer to the VMware Security Advisory VMSA-2022-0004.

Detection Methods for CVE-2021-22042

Indicators of Compromise

Unexpected process communication between VMX processes and the settingsd service
Anomalous authentication attempts to settingsd from VMX process contexts
Unusual privilege escalation patterns on ESXi hosts
Log entries indicating VMX processes accessing settingsd authorization mechanisms

Detection Strategies

Monitor ESXi host logs for unusual inter-process communication patterns involving VMX and settingsd
Implement behavioral analysis to detect privilege escalation attempts on virtualization infrastructure
Deploy endpoint detection solutions capable of monitoring ESXi host activity
Review authentication logs for the settingsd service for unauthorized access attempts

Monitoring Recommendations

Enable verbose logging on ESXi hosts to capture detailed process interaction data
Configure alerting for authentication anomalies within the ESXi management stack
Implement centralized log collection for all VMware infrastructure components
Regularly audit VMX process behavior and settingsd service access patterns

How to Mitigate CVE-2021-22042

Immediate Actions Required

Apply VMware security patches as outlined in VMSA-2022-0004 immediately
Audit VMware ESXi 7.0 and Cloud Foundation deployments for exposure
Restrict network and administrative access to ESXi management interfaces
Review existing virtual machine configurations for potential compromise indicators

Patch Information

VMware has released security updates to address this vulnerability. Organizations should consult the VMware Security Advisory VMSA-2022-0004 for specific patch versions and update instructions. Patches should be applied to all affected VMware ESXi 7.0 Update 1, Update 2, and Update 3 systems, as well as affected VMware Cloud Foundation deployments.

Workarounds

Limit administrative access to ESXi hosts to trusted personnel only
Implement network segmentation to isolate VMware management interfaces
Deploy additional monitoring on ESXi hosts until patches can be applied
Consider temporarily restricting VM deployment capabilities in high-security environments

bash

# Verify ESXi version and update status
esxcli system version get

# Check for available updates
esxcli software profile update --dry-run --depot=<update_depot_url>

# Review settingsd service logs for anomalies
cat /var/log/settingsd.log | grep -i "auth\|error\|warning"