CVE-2021-21513: Dell OMSA Auth Bypass Vulnerability

CVE-2021-21513 Overview

Dell EMC OpenManage Server Administrator (OMSA) version 9.5 Microsoft Windows installations with Distributed Web Server (DWS) enabled configuration contains an authentication bypass vulnerability. A remote unauthenticated attacker could potentially exploit this vulnerability to gain admin access on the affected system.

Critical Impact

This authentication bypass vulnerability allows remote unauthenticated attackers to gain administrative access to Dell EMC OpenManage Server Administrator, potentially leading to complete system compromise of managed servers.

Affected Products

• Dell OpenManage Server Administrator version 9.5 on Microsoft Windows
• Dell OMSA installations with Distributed Web Server (DWS) enabled
• Dell EMC server management infrastructure using vulnerable OMSA versions

Discovery Timeline

• 2021-03-02 - CVE-2021-21513 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-21513

Vulnerability Analysis

This vulnerability is classified as CWE-287 (Improper Authentication), which occurs when the application does not properly verify the identity of users attempting to access protected resources. In the context of Dell EMC OpenManage Server Administrator, the Distributed Web Server (DWS) component fails to properly enforce authentication controls, allowing remote attackers to bypass the authentication mechanism entirely.

The attack can be conducted remotely over the network without requiring any prior authentication or user interaction. When successfully exploited, an attacker gains complete administrative control over the OMSA instance, which provides extensive management capabilities over the underlying Dell EMC server hardware. This includes the ability to modify system configurations, access sensitive server information, and potentially pivot to other systems in the enterprise environment.

Root Cause

The root cause of this vulnerability lies in improper authentication handling within the Distributed Web Server (DWS) component of Dell EMC OpenManage Server Administrator. When DWS is enabled on Windows installations, the authentication validation logic fails to properly verify user credentials before granting access to administrative functions. This authentication bypass occurs due to flawed session management or credential verification logic in the web server component.

Attack Vector

The vulnerability is exploitable remotely over the network. An attacker with network access to the OMSA web interface can exploit this vulnerability without requiring any valid credentials or user interaction. The attack targets the Distributed Web Server component, which when enabled, exposes the authentication bypass condition.

The exploitation flow involves:

1. Identifying Dell OMSA installations with DWS enabled (typically accessible via web interface)
2. Sending crafted requests that bypass the authentication mechanism
3. Gaining administrative access to the OMSA management console
4. Leveraging admin privileges to modify server configurations or access sensitive data

For detailed technical analysis, refer to the Tenable Security Research TRA-2021-07 advisory.

Detection Methods for CVE-2021-21513

Indicators of Compromise

• Unexpected administrative sessions or login events in OMSA logs without corresponding valid authentication
• Anomalous access patterns to the OMSA web interface from external or unauthorized IP addresses
• Configuration changes to Dell EMC server hardware settings without authorized administrator activity
• Suspicious HTTP requests to OMSA endpoints that bypass normal authentication flows

Detection Strategies

• Monitor network traffic to OMSA web interfaces for unusual authentication patterns or direct access to administrative endpoints
• Review OMSA application logs for authentication anomalies and unauthorized administrative actions
• Implement network segmentation monitoring to detect unauthorized access attempts to management interfaces
• Deploy web application firewalls with rules to detect authentication bypass attempts

Monitoring Recommendations

• Enable detailed logging on Dell OMSA instances and forward logs to a centralized SIEM solution
• Configure alerts for administrative actions performed without corresponding successful authentication events
• Monitor for unauthorized network connections to OMSA management ports
• Perform regular audits of OMSA user accounts and administrative session activity

How to Mitigate CVE-2021-21513

Immediate Actions Required

• Upgrade Dell EMC OpenManage Server Administrator to a patched version as specified in DSA-2021-040
• If immediate patching is not possible, disable the Distributed Web Server (DWS) feature on affected Windows installations
• Restrict network access to OMSA management interfaces using firewall rules or network segmentation
• Review OMSA logs for any signs of prior exploitation or unauthorized access

Patch Information

Dell has released security updates to address this vulnerability as documented in Dell Security Advisory DSA-2021-040. Administrators should apply the latest available version of Dell EMC OpenManage Server Administrator that addresses CVE-2021-21513. The security advisory provides detailed remediation guidance and links to updated software packages.

Workarounds

• Disable the Distributed Web Server (DWS) feature if it is not required for operations
• Implement strict network access controls to limit exposure of OMSA management interfaces to authorized networks only
• Use a VPN or jump server to access OMSA interfaces rather than exposing them directly to broader network segments
• Enable additional authentication mechanisms such as multi-factor authentication at the network perimeter level

# Configuration example - Restrict OMSA access via Windows Firewall
# Block external access to OMSA web interface (default port 1311)
netsh advfirewall firewall add rule name="Block OMSA External" dir=in action=block protocol=tcp localport=1311 remoteip=any
# Allow access only from management network
netsh advfirewall firewall add rule name="Allow OMSA Management" dir=in action=allow protocol=tcp localport=1311 remoteip=10.0.0.0/8