CVE-2016-8744 in Brooklyn
Summary
by MITRE
Apache Brooklyn uses the SnakeYAML library for parsing YAML inputs. SnakeYAML allows the use of YAML tags to indicate that SnakeYAML should unmarshal data to a Java type. In the default configuration in Brooklyn before 0.10.0, SnakeYAML will allow unmarshalling to any Java type available on the classpath. This could provide an authenticated user with a means to cause the JVM running Brooklyn to load and run Java code without detection by Brooklyn. Such code would have the privileges of the Java process running Brooklyn, including the ability to open files and network connections, and execute system commands. There is known to be a proof-of-concept exploit using this vulnerability.
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Analysis
by VulDB Data Team • 11/15/2019
Apache Brooklyn represents a powerful application deployment and management platform that leverages YAML for configuration and orchestration purposes. The vulnerability described in CVE-2016-8744 stems from Brooklyn's reliance on the SnakeYAML library for processing YAML input data. This dependency introduces a critical security flaw where the default SnakeYAML configuration permits unmarshalling operations to any Java type accessible within the application's classpath. The vulnerability exists because Brooklyn's implementation fails to properly restrict the types that can be instantiated during YAML parsing, creating an attack surface that allows maliciously crafted YAML content to trigger arbitrary code execution.
The technical flaw manifests when an authenticated user submits specially crafted YAML input that includes YAML tags referencing specific Java classes. In the vulnerable versions prior to 0.10.0, SnakeYAML's default settings do not implement proper type filtering or restriction mechanisms. This configuration allows the unmarshalling process to instantiate any Java class present in the classpath, effectively bypassing normal security boundaries. The attack vector exploits the inherent flexibility of YAML's type system while undermining the security assumptions of the Brooklyn platform. The vulnerability is particularly dangerous because it operates within the context of the running JVM, meaning that any code executed inherits the privileges and permissions of the Brooklyn process itself.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it provides attackers with complete control over the affected system. When exploited, the malicious code can perform any operation that the Brooklyn process is authorized to perform, including reading and writing files, establishing network connections, and executing system commands. This level of access enables attackers to potentially exfiltrate sensitive data, establish persistence mechanisms, or use the compromised system as a launch point for further attacks within the network. The vulnerability is particularly concerning because it operates without detection by Brooklyn's own security mechanisms, making it difficult to identify when an attack has occurred. The existence of known proof-of-concept exploits demonstrates that this vulnerability is not merely theoretical but represents an active threat that has been weaponized by threat actors.
The mitigation strategy for CVE-2016-8744 requires immediate patching of Brooklyn installations to version 0.10.0 or later, which includes enhanced SnakeYAML configuration that restricts type instantiation. Organizations should implement proper input validation and sanitization measures for all YAML processing within their systems. The vulnerability aligns with CWE-502, which specifically addresses deserialization of untrusted data, and relates to ATT&CK technique T1059 for command and scripting interpreter usage. Security teams should also consider implementing network segmentation and monitoring for unusual file access patterns or outbound network connections that might indicate exploitation attempts. Regular security assessments of all applications using SnakeYAML or similar libraries are essential to prevent similar vulnerabilities from emerging in other components of the software stack.