CVE-2021-33708 in Kyma
Summary
by MITRE • 08/11/2021
Due to insufficient input validation in Kyma, authenticated users can pass a Header of their choice and escalate privileges.
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Analysis
by VulDB Data Team • 08/16/2021
The vulnerability identified as CVE-2021-33708 represents a critical privilege escalation flaw within the Kyma platform, an open-source Kubernetes-based application development framework. This vulnerability specifically affects authenticated users who can manipulate HTTP headers to gain elevated privileges within the system. The issue stems from inadequate input validation mechanisms that fail to properly sanitize or verify header values before processing them within the application's authorization framework. The flaw exists at the intersection of web application security and identity management, where improper header handling creates an attack vector for unauthorized privilege elevation.
The technical implementation of this vulnerability allows authenticated attackers to craft malicious HTTP requests containing specially crafted headers that bypass normal access controls. When the Kyma platform processes these headers without proper validation, it can interpret them as legitimate authorization tokens or identity claims, effectively allowing users to assume roles or permissions beyond their normal access levels. This type of vulnerability aligns with CWE-20, which covers improper input validation, and specifically demonstrates how header manipulation can lead to authorization bypass scenarios. The flaw operates at the application layer where HTTP headers are processed for authentication decisions rather than being properly validated against expected formats or values.
The operational impact of CVE-2021-33708 extends beyond simple privilege escalation, as it can enable attackers to access sensitive data, modify system configurations, or potentially gain administrative control over the Kyma environment. This vulnerability particularly affects organizations using Kyma for enterprise application development, as it undermines the trust model that the platform relies upon for maintaining secure multi-tenant environments. Attackers could leverage this vulnerability to access other users' resources, escalate their access to system-level operations, or potentially use the elevated privileges to deploy malicious code within the Kubernetes cluster. The impact is exacerbated by the fact that the vulnerability requires only authentication, making it accessible to users who have legitimate access to the system but should not possess elevated privileges.
Organizations should implement immediate mitigations including comprehensive header validation, implementing strict input sanitization for all HTTP headers, and deploying proper authorization controls that do not rely solely on header values. The solution involves configuring the Kyma platform to validate header contents against predefined schemas and reject any headers that do not conform to expected patterns. Security teams should also consider implementing additional monitoring and logging around header processing to detect anomalous behavior. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and specifically relates to T1078, which covers valid accounts and T1548, which covers abuse of privileges. Organizations should also review their authentication and authorization mechanisms to ensure that header-based authentication is properly secured and that access controls are implemented at multiple layers of the application architecture.