CVE-2018-5256 in CoreOS Tectonic
Summary
by MITRE
CoreOS Tectonic 1.7.x before 1.7.9-tectonic.4 and 1.8.x before 1.8.4-tectonic.3 mounts a direct proxy to the kubernetes cluster at /api/kubernetes/ which is accessible without authentication to Tectonic and allows an attacker to directly connect to the kubernetes API server. Unauthenticated users are able to list all Namespaces through the Console, resulting in an information disclosure. Tectonic's exposure of an unauthenticated API endpoint containing information regarding the internal state of the cluster can provide an attacker with information that may assist in other attacks against the cluster. For example, an attacker may not have the permissions required to list all namespaces in the cluster but can instead leverage this vulnerability to enumerate the namespaces and then begin to check each namespace for weak authorization policies that may allow further escalation of privileges.
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Analysis
by VulDB Data Team • 02/07/2020
The vulnerability described in CVE-2018-5256 represents a critical authentication bypass flaw within CoreOS Tectonic versions prior to 1.7.9-tectonic.4 and 1.8.4-tectonic.3. This issue stems from the improper configuration of the Tectonic console interface which exposes a direct proxy endpoint at /api/kubernetes/ without requiring any form of authentication or authorization. The flaw allows unauthenticated attackers to establish connections directly to the underlying Kubernetes API server, effectively creating an unauthorized access point to the cluster's internal state information. This configuration violates fundamental security principles of least privilege and proper access control enforcement within container orchestration environments.
The technical implementation of this vulnerability involves the Tectonic console application mounting a proxy endpoint that directly forwards requests to the Kubernetes API server without validating user credentials or roles. This direct proxy mechanism bypasses the normal authentication mechanisms that should protect cluster resources. When attackers access the exposed endpoint, they can enumerate all namespaces within the cluster through the console interface, which constitutes a significant information disclosure vulnerability. The namespace enumeration capability provides attackers with comprehensive visibility into the cluster's organizational structure and resource distribution, including potential sensitive namespaces that may contain confidential applications or workloads. This information disclosure aligns with CWE-200 (Information Exposure) and represents a classic example of how improper access controls can lead to reconnaissance capabilities for attackers.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it enables attackers to conduct comprehensive reconnaissance and planning for subsequent attacks against the cluster. The enumeration of namespaces provides attackers with knowledge of cluster topology, which can be leveraged to identify potential targets for privilege escalation or lateral movement. An attacker who cannot directly list namespaces through normal Kubernetes API permissions can instead exploit this vulnerability to gain the same information, potentially leading to more sophisticated attacks such as identifying namespaces with weak authorization policies, locating sensitive workloads, or discovering applications that may contain vulnerabilities. This vulnerability directly relates to ATT&CK technique T1069.001 (Credential Access: Account Discovery) and T1087.001 (Account Access: Local Account) as it enables unauthorized access to cluster resources that would normally require proper authentication and authorization.
The security implications of this vulnerability are particularly concerning in enterprise environments where Kubernetes clusters often contain multiple namespaces with varying levels of sensitivity and access control. The exposure of namespace information can enable attackers to map out the entire cluster landscape and identify potential attack vectors that might not be immediately apparent through normal operational procedures. Organizations using affected Tectonic versions face increased risk of privilege escalation attacks, as the namespace enumeration capability can reveal which namespaces contain applications with elevated privileges or sensitive data. This vulnerability essentially provides attackers with a roadmap for cluster exploration and can significantly reduce the time and effort required to conduct successful attacks. Organizations should consider implementing network segmentation, proper access controls, and monitoring of unusual API access patterns as part of their defense-in-depth strategies. The vulnerability underscores the importance of proper endpoint configuration and authentication enforcement in container orchestration platforms, particularly when exposing proxy mechanisms that bypass normal security controls.