CVE-2021-22011: VMware vCenter Auth Bypass Vulnerability

CVE-2021-22011 Overview

CVE-2021-22011 is an unauthenticated API endpoint vulnerability affecting VMware vCenter Server Content Library. A malicious actor with network access to port 443 on vCenter Server may exploit this issue to perform unauthenticated VM network setting manipulation. This vulnerability allows attackers to bypass authentication controls and directly interact with sensitive API endpoints that should require proper authorization.

Critical Impact

Unauthenticated attackers with network access to vCenter Server port 443 can manipulate VM network settings without credentials, potentially enabling network-based attacks, lateral movement, or disruption of virtual machine connectivity.

Affected Products

• VMware vCenter Server 6.5
• VMware vCenter Server 6.7
• VMware vCenter Server 7.0
• VMware Cloud Foundation (multiple versions)

Discovery Timeline

• 2021-09-23 - CVE-2021-22011 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-22011

Vulnerability Analysis

This vulnerability exists within the vCenter Server Content Library component, specifically in an API endpoint that fails to enforce proper authentication. The Content Library is a centralized repository in vCenter Server used to store and manage VM templates, ISO images, and other deployment assets. Due to improper access control on certain API endpoints, an attacker can interact with these endpoints without providing valid credentials.

The vulnerability enables manipulation of VM network settings, which could have significant implications for virtualized infrastructure. An attacker exploiting this flaw could potentially modify network configurations for virtual machines, redirect network traffic, or disrupt connectivity between VMs and the broader network infrastructure. This type of access could facilitate further attacks within the virtualized environment.

Root Cause

The root cause of CVE-2021-22011 is insufficient authentication enforcement on specific API endpoints within the vCenter Server Content Library. The affected endpoints were exposed without requiring proper credential validation, allowing unauthenticated network requests to be processed. This represents a broken access control vulnerability where authentication checks were missing or improperly implemented for sensitive administrative functions.

Attack Vector

The attack vector for this vulnerability is network-based, targeting port 443 (HTTPS) on the vCenter Server. An attacker requires network connectivity to the vCenter Server management interface but does not need valid credentials or any prior authentication. The attack can be executed remotely by any actor who can reach the vCenter Server over the network.

The exploitation process involves sending specially crafted HTTP requests to the vulnerable API endpoints. Since authentication is not enforced, the attacker's requests are processed as if they were legitimate administrative operations, allowing manipulation of VM network configurations. The low complexity of exploitation combined with no authentication requirement makes this vulnerability accessible to a wide range of threat actors.

Detection Methods for CVE-2021-22011

Indicators of Compromise

• Unusual API requests to vCenter Server Content Library endpoints from unexpected source IP addresses
• Unexpected modifications to VM network settings without corresponding administrative activity
• Authentication logs showing API access without proper authentication tokens
• Network traffic anomalies on port 443 targeting vCenter Server with unusual request patterns

Detection Strategies

• Monitor vCenter Server logs for API calls to Content Library endpoints that lack authentication context
• Implement network intrusion detection rules to identify suspicious request patterns targeting vCenter Server APIs
• Deploy behavioral analytics to detect unauthorized configuration changes to VM network settings
• Review vCenter Server access logs for requests originating from untrusted or unexpected network segments

Monitoring Recommendations

• Enable verbose logging on vCenter Server to capture detailed API request information
• Configure SIEM alerts for unauthenticated access attempts to administrative endpoints
• Implement network segmentation monitoring to detect lateral movement attempts following exploitation
• Establish baseline network behavior for vCenter Server and alert on deviations

How to Mitigate CVE-2021-22011

Immediate Actions Required

• Apply VMware security patches as outlined in VMSA-2021-0020 immediately
• Restrict network access to vCenter Server port 443 to trusted administrative networks only
• Implement firewall rules to limit exposure of the vCenter Server management interface
• Audit current VM network configurations for unauthorized changes

Patch Information

VMware has released security updates to address this vulnerability. Administrators should consult the VMware Security Advisory VMSA-2021-0020 for detailed patch information and remediation guidance. The advisory provides specific version numbers containing the fix for vCenter Server 6.5, 6.7, and 7.0 releases, as well as guidance for VMware Cloud Foundation deployments.

Workarounds

• Implement strict network segmentation to isolate vCenter Server from untrusted network segments
• Deploy a web application firewall (WAF) or API gateway to filter malicious requests to vCenter Server endpoints
• Use VPN or jump host requirements for all administrative access to vCenter Server
• Consider implementing additional authentication layers such as multi-factor authentication for vCenter Server access
• Monitor and restrict outbound network connectivity from the vCenter Server to detect and prevent potential data exfiltration

# Example firewall rule to restrict vCenter Server access
# Allow only trusted administrative networks to access port 443
iptables -A INPUT -p tcp --dport 443 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP