CVE-2021-23018 in Controller
Summary
by MITRE • 06/01/2021
Intra-cluster communication does not use TLS. The services within the NGINX Controller 3.x before 3.4.0 namespace are using cleartext protocols inside the cluster.
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Analysis
by VulDB Data Team • 06/03/2021
The vulnerability identified as CVE-2021-23018 affects NGINX Controller version 3.x prior to 3.4.0, specifically addressing a critical weakness in intra-cluster communication security. This flaw represents a significant deviation from established security best practices where internal service communications should be encrypted to prevent unauthorized access and data interception. The issue manifests when services operating within the same namespace fail to implement Transport Layer Security protocols for their internal communications, leaving sensitive data and control messages exposed to potential eavesdropping attacks.
The technical implementation flaw stems from the absence of encrypted communication channels between microservices and components within the NGINX Controller cluster environment. This cleartext communication pattern creates multiple attack vectors for malicious actors who may have gained access to the internal network or compromised nodes within the cluster. The vulnerability directly violates security principles outlined in the OWASP Top Ten and aligns with CWE-319, which specifically addresses cleartext transmission of sensitive information. When services communicate without TLS encryption, they become susceptible to man-in-the-middle attacks, session hijacking, and unauthorized data extraction from internal communication channels.
The operational impact of this vulnerability extends beyond simple data exposure, as it fundamentally undermines the security posture of the entire NGINX Controller deployment. Attackers who can intercept internal communications may gain access to sensitive configuration data, authentication tokens, and operational parameters that could be leveraged to escalate privileges or compromise additional system components. This vulnerability particularly affects organizations that rely on NGINX Controller for API management and traffic control, as the exposed internal communications could provide attackers with insights into service endpoints, routing configurations, and potentially sensitive business logic. The risk is compounded in multi-tenant environments where isolation between different services is compromised due to the lack of encrypted inter-service communication.
Organizations should immediately implement mitigations including upgrading to NGINX Controller version 3.4.0 or later, which addresses this vulnerability through the enforcement of TLS encryption for all intra-cluster communications. Additionally, network segmentation and firewall rules should be implemented to limit access to the controller cluster, while monitoring systems should be deployed to detect unusual communication patterns that might indicate attempted exploitation. From an ATT&CK framework perspective, this vulnerability maps to T1046 Network Service Scanning and T1566 Impersonation, as attackers can leverage the cleartext communications to discover service endpoints and potentially impersonate legitimate services. The remediation process should also include comprehensive security assessments of all internal communication channels to ensure that similar vulnerabilities do not exist in other components of the infrastructure.