CVE-2020-8553 in Kubernetes
Summary
by MITRE
The Kubernetes ingress-nginx component prior to version 0.28.0 allows a user with the ability to create namespaces and to read and create ingress objects to overwrite the password file of another ingress which uses nginx.ingress.kubernetes.io/auth-type: basic and which has a hyphenated namespace or secret name.
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Analysis
by VulDB Data Team • 11/06/2020
The vulnerability identified as CVE-2020-8553 affects the ingress-nginx component within Kubernetes environments, specifically impacting versions prior to 0.28.0. This security flaw resides in the handling of basic authentication configurations where ingress controllers manage access control through password files stored in the filesystem. The vulnerability stems from improper path handling when processing ingress resources that utilize basic authentication with nginx.ingress.kubernetes.io/auth-type: basic annotation, creating a scenario where namespace and secret naming conventions can be exploited to manipulate file system operations.
The technical implementation of this vulnerability exploits a predictable path construction mechanism within the ingress-nginx controller that does not properly sanitize or validate namespace and secret names containing hyphens. When an attacker creates a namespace or secret with hyphens in the name, the controller's path generation logic can produce paths that inadvertently target or overwrite existing password files belonging to other ingress resources. This occurs because the controller's file system operations do not adequately distinguish between different ingress configurations, particularly when dealing with naming conventions that include special characters like hyphens. The flaw essentially allows for a form of path traversal or file system manipulation that bypasses normal access controls.
The operational impact of this vulnerability is significant within multi-tenant Kubernetes environments where different teams or applications might share the same cluster but require isolated authentication mechanisms. An attacker with minimal privileges - specifically the ability to create namespaces and manipulate ingress objects - can escalate their access level by overwriting authentication files of other ingress resources. This creates a privilege escalation scenario where one user can potentially gain access to resources belonging to other users or applications, effectively breaking the isolation guarantees that Kubernetes security models typically provide. The vulnerability undermines the fundamental security principle of least privilege by allowing unauthorized access to authentication credentials.
The vulnerability aligns with CWE-22 Path Traversal and CWE-73 Path Traversal, both of which address improper handling of file system paths that can lead to unauthorized access to resources. From an ATT&CK perspective, this vulnerability maps to T1078 Valid Accounts and T1566 Phishing, as it can be exploited to gain access to authentication credentials that would otherwise be protected. The attack vector requires the attacker to have sufficient permissions to create namespaces and ingress objects, which represents a moderate privilege requirement but is achievable in many shared cluster environments. Organizations should implement the remediation of updating to ingress-nginx version 0.28.0 or later, which includes proper path sanitization and validation. Additional mitigations include implementing stricter RBAC policies to limit namespace creation privileges, monitoring ingress resource changes, and conducting regular security audits of authentication configurations. Organizations should also consider implementing network segmentation and additional monitoring controls to detect anomalous file system operations that might indicate exploitation attempts.