CVE-2018-20133 in ymlref
Summary
by MITRE
ymlref allows code injection.
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Analysis
by VulDB Data Team • 04/21/2020
The vulnerability identified as CVE-2018-20133 affects the ymlref tool, which is designed to process and reference yaml files in various applications. This tool is commonly used in configuration management and automation workflows where yaml files serve as data sources for system configurations, deployment scripts, and application settings. The vulnerability stems from insufficient input validation and sanitization mechanisms within the ymlref processing engine, creating a path for malicious actors to inject arbitrary code during the yaml parsing operation.
The technical flaw manifests when ymlref processes yaml files containing specially crafted payloads that exploit the tool's handling of certain yaml directives and data structures. Specifically, the vulnerability allows for code injection through improper sanitization of user-supplied yaml content, enabling attackers to execute arbitrary commands on systems where ymlref is deployed. This occurs because the tool does not adequately validate or escape yaml content before processing, particularly when encountering complex yaml constructs such as anchors, aliases, or custom tags that can be manipulated to trigger unintended execution paths. The vulnerability is classified under CWE-94, which addresses "Improper Control of Generation of Code," and aligns with ATT&CK technique T1059.006 for "Command and Scripting Interpreter: PowerShell" and T1059.001 for "Command and Scripting Interpreter: Command Shell" when attackers leverage the injection to execute system commands.
The operational impact of this vulnerability is significant across multiple attack vectors and system environments. Organizations using ymlref in continuous integration/continuous deployment pipelines, configuration management systems, or automated provisioning workflows face potential compromise when processing untrusted yaml content. Attackers could exploit this vulnerability to execute malicious code on build servers, deployment systems, or target hosts where ymlref is installed and used. The vulnerability particularly affects environments where yaml files are processed from external sources without proper validation, including automated systems that fetch configuration files from remote repositories or user-provided inputs. The risk is amplified when ymlref operates with elevated privileges or in environments where the executed code could access sensitive system resources, databases, or network services.
Mitigation strategies for CVE-2018-20133 require a multi-layered approach focusing on input validation, privilege management, and environment hardening. Organizations should immediately update to patched versions of ymlref where available, as the vulnerability was addressed through improved input sanitization and stricter yaml parsing controls. System administrators should implement strict access controls limiting where and how ymlref can be executed, ensuring it operates with minimal required privileges and in isolated environments. Input validation measures must be strengthened to reject or sanitize yaml content containing suspicious constructs, particularly those involving anchors, aliases, or custom tags that could enable code injection. Network segmentation and monitoring solutions should be deployed to detect anomalous execution patterns or unauthorized code execution attempts. Additionally, implementing automated scanning tools that can identify potentially malicious yaml content before processing would provide an additional layer of protection. Organizations should also consider alternative configuration management approaches that do not rely on potentially vulnerable yaml parsing libraries, particularly for critical systems where the risk of code injection could have severe operational consequences. The remediation process should include comprehensive testing of yaml processing workflows to ensure that all input sources are properly validated before any yaml content is processed by the ymlref tool.