CVE-2021-21998: VMware Carbon Black Authentication Bypass

CVE-2021-21998 Overview

CVE-2021-21998 is a critical authentication bypass vulnerability affecting VMware Carbon Black App Control, an endpoint security solution used for application whitelisting and control. This vulnerability allows a malicious actor with network access to the VMware Carbon Black App Control management server to potentially obtain administrative access to the product without the need to authenticate.

The vulnerability is classified under CWE-287 (Improper Authentication), indicating a fundamental flaw in the authentication mechanism that fails to properly verify user identity before granting access to protected resources.

Critical Impact

Unauthenticated attackers with network access to the management server can gain full administrative control over the Carbon Black App Control environment, potentially compromising endpoint security across the entire organization.

Affected Products

• VMware Carbon Black App Control 8.0
• VMware Carbon Black App Control 8.1
• VMware Carbon Black App Control 8.5 prior to 8.5.8
• VMware Carbon Black App Control 8.6 prior to 8.6.2

Discovery Timeline

• 2021-06-23 - CVE CVE-2021-21998 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-21998

Vulnerability Analysis

This authentication bypass vulnerability affects the management server component of VMware Carbon Black App Control. The flaw enables remote attackers to circumvent the authentication process entirely, gaining administrative privileges without providing valid credentials.

The attack can be executed remotely over the network without requiring any prior authentication or user interaction. Once exploited, an attacker gains complete control over the Carbon Black App Control management console, which could lead to:

• Disabling endpoint protection across managed systems
• Modifying application whitelisting policies
• Accessing sensitive security configuration data
• Using the compromised security infrastructure as a pivot point for further attacks

Root Cause

The root cause of this vulnerability lies in improper authentication handling within the Carbon Black App Control management server. The authentication mechanism fails to properly validate or enforce authentication requirements under certain conditions, allowing attackers to bypass security controls designed to verify user identity.

This type of authentication bypass typically occurs when:

• Authentication checks are not consistently applied across all access paths
• Session management contains logic flaws that can be exploited
• Request handling improperly processes authentication tokens or credentials

Attack Vector

The attack vector is network-based, meaning any attacker with network connectivity to the Carbon Black App Control management server can potentially exploit this vulnerability. The attack requires no privileges, no user interaction, and has low complexity to execute.

Organizations exposing their Carbon Black App Control management servers to untrusted networks or the internet are at heightened risk. The vulnerability allows attackers to bypass authentication mechanisms through specially crafted requests to the management server interface.

Given the nature of this vulnerability as an authentication bypass in a security management product, exploitation techniques would target the authentication workflow of the management console. For detailed technical information regarding the specific attack methodology, refer to the VMware Security Advisory VMSA-2021-0012.

Detection Methods for CVE-2021-21998

Indicators of Compromise

• Unexpected administrative sessions or logins to the Carbon Black App Control management console without corresponding legitimate authentication events
• Unauthorized changes to application control policies or whitelist configurations
• Anomalous network traffic patterns targeting the Carbon Black App Control management server ports
• Log entries showing administrative actions without proper authentication trails

Detection Strategies

• Monitor authentication logs for administrative access events that lack corresponding credential validation entries
• Implement network-based detection for unusual connection patterns to the management server
• Deploy SentinelOne Singularity platform to detect anomalous endpoint behavior that may indicate compromised Carbon Black deployments
• Configure SIEM alerts for policy changes or administrative actions occurring outside normal business hours or from unexpected source IPs

Monitoring Recommendations

• Enable comprehensive logging on Carbon Black App Control management servers and forward logs to a centralized SIEM
• Monitor network traffic to and from the management server for signs of exploitation attempts
• Implement real-time alerting for any unauthorized administrative access or configuration changes
• Conduct regular audits of administrative accounts and their activity within the Carbon Black environment

How to Mitigate CVE-2021-21998

Immediate Actions Required

• Immediately restrict network access to Carbon Black App Control management servers to trusted administrative networks only
• Apply vendor-provided security patches as soon as possible
• Review administrative access logs for any signs of unauthorized access
• Implement network segmentation to isolate management infrastructure from general network traffic
• Consider temporarily disabling external access to the management console until patching is complete

Patch Information

VMware has released patched versions to address this vulnerability. Organizations should upgrade to the following fixed versions:

• Carbon Black App Control 8.5.8 or later for the 8.5.x branch
• Carbon Black App Control 8.6.2 or later for the 8.6.x branch

For complete patch details and download information, refer to the VMware Security Advisory VMSA-2021-0012.

Workarounds

• Implement strict network access controls limiting management server connectivity to authorized administrative workstations only
• Deploy a VPN or jump server requirement for all administrative access to the Carbon Black App Control management console
• Enable firewall rules to restrict inbound connections to the management server from untrusted networks
• Monitor and audit all administrative access attempts while awaiting patch deployment

# Example: Restrict network access to management server using iptables
# Allow only trusted admin network (example: 10.0.1.0/24) to access management port
iptables -A INPUT -p tcp --dport 443 -s 10.0.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

# Log any blocked connection attempts for monitoring
iptables -A INPUT -p tcp --dport 443 -j LOG --log-prefix "CB_MGMT_BLOCKED: "