CVE-2020-2121 in Google Kubernetes Engine Plugin
Summary
by MITRE
Jenkins Google Kubernetes Engine Plugin 0.8.0 and earlier does not configure its YAML parser to prevent the instantiation of arbitrary types, resulting in a remote code execution vulnerability.
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Analysis
by VulDB Data Team • 02/13/2020
The vulnerability identified as CVE-2020-2121 affects the Jenkins Google Kubernetes Engine Plugin version 0.8.0 and earlier, presenting a critical remote code execution risk through improper YAML parsing configuration. This flaw resides in the plugin's handling of YAML input data structures, specifically failing to restrict type instantiation during parsing operations. The vulnerability allows attackers to craft malicious YAML payloads that can trigger the deserialization of arbitrary Java classes, potentially enabling remote code execution on Jenkins servers running affected plugin versions.
The technical root cause of this vulnerability maps directly to CWE-502, which addresses deserialization of untrusted data, and more specifically CWE-470, dealing with the use of insecure deserialization mechanisms. The plugin's YAML parser configuration lacks proper type filtering or restriction mechanisms, allowing attackers to inject malicious type definitions that bypass normal security boundaries. When Jenkins processes these specially crafted YAML files through the affected plugin, the parser inadvertently instantiates attacker-controlled Java classes, creating a pathway for arbitrary code execution within the Jenkins environment. This represents a classic deserialization vulnerability where untrusted input flows directly into object instantiation without adequate sanitization or validation.
The operational impact of this vulnerability extends beyond simple remote code execution, as it can enable full system compromise of Jenkins servers that are configured with vulnerable plugin versions. Attackers can leverage this vulnerability to execute arbitrary commands with the privileges of the Jenkins process, potentially gaining access to build artifacts, source code repositories, and other sensitive data stored within the Jenkins environment. The vulnerability affects both the Jenkins master and any agents that might be processing the malicious YAML content, creating a broad attack surface. Additionally, since Jenkins is commonly used in CI/CD pipelines, successful exploitation could lead to supply chain compromise, allowing attackers to inject malicious code into legitimate build processes and potentially affect downstream systems and deployments.
Organizations should prioritize immediate remediation by upgrading to Jenkins Google Kubernetes Engine Plugin version 0.8.1 or later, which includes proper YAML parser configuration to prevent instantiation of arbitrary types. System administrators should also implement network-level restrictions to limit access to Jenkins servers, particularly those with Kubernetes plugin functionality enabled. The mitigation strategy should include monitoring for suspicious YAML content and implementing proper input validation for all external data sources. Security teams should consider implementing runtime protection mechanisms and network segmentation to reduce the potential impact of successful exploitation attempts. This vulnerability also highlights the importance of following secure coding practices around deserialization and input handling, as outlined in the mitre attack framework under techniques related to deserialization attacks and remote code execution. Organizations should conduct comprehensive vulnerability assessments to identify all instances of the affected plugin across their infrastructure and ensure proper patch management processes are in place to prevent similar issues in the future.