CVE-2021-1388 Overview
A critical authentication bypass vulnerability exists in Cisco ACI Multi-Site Orchestrator (MSO) when installed on the Application Services Engine. This flaw allows an unauthenticated, remote attacker to bypass authentication mechanisms on affected devices by exploiting improper token validation on a specific API endpoint. By sending a crafted request to the vulnerable API, an attacker can obtain a token with administrator-level privileges, enabling full authentication to both the MSO and managed Cisco Application Policy Infrastructure Controller (APIC) devices.
Critical Impact
Unauthenticated attackers can gain administrator-level access to Cisco ACI Multi-Site Orchestrator and managed APIC devices, potentially compromising entire data center network infrastructure.
Affected Products
- Cisco ACI Multi-Site Orchestrator (versions prior to 3.0(3j))
- Cisco Application Policy Infrastructure Controller (APIC) 3.0(3i)
- Application Services Engine deployments with MSO installed
Discovery Timeline
- 2021-02-24 - CVE-2021-1388 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2021-1388
Vulnerability Analysis
This authentication bypass vulnerability stems from improper token validation within a specific API endpoint of Cisco ACI Multi-Site Orchestrator. The flaw is classified under CWE-269 (Improper Privilege Management), indicating a fundamental weakness in how the application handles authentication tokens and privilege assignment.
When successfully exploited, attackers can receive tokens with administrator-level privileges without providing valid credentials. This grants unauthorized access to both the MSO management interface and any connected APIC devices, effectively providing full control over the multi-site data center fabric orchestration platform.
The vulnerability is particularly severe because Cisco ACI Multi-Site Orchestrator is designed to manage policies across multiple Application Centric Infrastructure (ACI) fabrics, meaning a single compromise could cascade across an organization's entire data center network infrastructure.
Root Cause
The root cause of CVE-2021-1388 is improper token validation on a specific API endpoint within the Cisco ACI Multi-Site Orchestrator. The application fails to properly verify authentication tokens before granting administrative privileges, allowing attackers to craft malicious requests that bypass the normal authentication flow. This represents a fundamental flaw in the authorization and session management mechanisms of the affected API.
Attack Vector
The attack vector for this vulnerability is network-based and requires no user interaction or prior authentication. An attacker can remotely target the vulnerable API endpoint by sending specially crafted HTTP requests. The exploitation process involves:
- Identifying an exposed Cisco ACI Multi-Site Orchestrator instance running on Application Services Engine
- Crafting a malicious request targeting the vulnerable API endpoint
- Bypassing authentication through improper token validation
- Receiving an administrator-level authentication token
- Using the obtained token to authenticate to MSO and managed APIC devices
The vulnerability mechanism exploits the improper token validation in the MSO API endpoint. When a crafted request is sent to this endpoint, the validation logic fails to properly verify the authenticity of the token request, allowing the attacker to receive administrator credentials. For detailed technical information, refer to the Cisco Security Advisory.
Detection Methods for CVE-2021-1388
Indicators of Compromise
- Unexpected administrator-level API authentications from unknown IP addresses
- Unusual token generation patterns in MSO authentication logs
- Unauthorized configuration changes to APIC policies or MSO settings
- API requests to authentication endpoints from external or untrusted networks
- Anomalous access patterns to the Application Services Engine management interface
Detection Strategies
- Monitor MSO and APIC authentication logs for unauthorized administrative access attempts
- Implement network traffic analysis to detect crafted requests targeting the vulnerable API endpoint
- Configure alerts for new administrator token generations outside normal business hours
- Review audit logs for configuration changes made by unexpected administrative sessions
- Deploy intrusion detection signatures specific to this vulnerability pattern
Monitoring Recommendations
- Enable verbose logging on Cisco ACI Multi-Site Orchestrator API endpoints
- Implement real-time alerting for failed and successful authentication events on MSO
- Monitor network traffic patterns to the Application Services Engine for anomalies
- Conduct regular reviews of administrative access logs across all managed APIC devices
- Integrate MSO logs with SIEM solutions for correlation and threat detection
How to Mitigate CVE-2021-1388
Immediate Actions Required
- Verify your Cisco ACI Multi-Site Orchestrator version and deployment type (only ASE deployments are affected)
- Apply the security patch from Cisco immediately if running a vulnerable version
- Restrict network access to the MSO management interface to trusted networks only
- Audit recent administrative access and configuration changes for signs of compromise
- Review and rotate administrative credentials on MSO and managed APIC devices
Patch Information
Cisco has released security patches to address this vulnerability. Organizations running Cisco ACI Multi-Site Orchestrator on Application Services Engine should upgrade to version 3.0(3j) or later immediately. The vulnerability does not affect MSO deployments on Nexus Dashboard (previously known as Nexus Fabric Controller). Detailed patch information is available in the Cisco Security Advisory cisco-sa-mso-authbyp-bb5GmBQv.
Workarounds
- No workarounds are available for this vulnerability according to Cisco
- Implement strict network segmentation to limit access to MSO management interfaces
- Deploy web application firewalls (WAF) to filter potentially malicious API requests
- Enable additional authentication factors where possible for administrative access
- Ensure MSO management interfaces are not exposed to untrusted networks
# Verify MSO version to determine vulnerability status
# Access MSO CLI and check current version
show version
# Restrict management access via ACLs (example)
ip access-list extended MSO-MANAGEMENT-RESTRICT
permit ip host TRUSTED_ADMIN_IP any
deny ip any any log
# Apply ACL to management interface
interface management
ip access-group MSO-MANAGEMENT-RESTRICT in
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
