CVE-2017-1000095 in Jenkins
Summary
by MITRE
The default whitelist included the following unsafe entries: DefaultGroovyMethods.putAt(Object, String, Object); DefaultGroovyMethods.getAt(Object, String). These allowed circumventing many of the access restrictions implemented in the script sandbox by using e.g. currentBuild['rawBuild'] rather than currentBuild.rawBuild. Additionally, the following entries allowed accessing private data that would not be accessible otherwise due to script security: groovy.json.JsonOutput.toJson(Closure); groovy.json.JsonOutput.toJson(Object).
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Analysis
by VulDB Data Team • 11/22/2019
The vulnerability identified as CVE-2017-1000095 represents a critical security flaw in Groovy script sandbox implementations that fundamentally undermines the security model designed to protect against unauthorized access and execution. This vulnerability resides in the default whitelist configuration that governs which methods and classes can be accessed within the sandboxed scripting environment. The issue stems from the inclusion of unsafe method entries in the whitelist that bypass the intended security boundaries, creating a pathway for attackers to escalate privileges and access restricted resources.
The technical flaw manifests through the inclusion of DefaultGroovyMethods.putAt and DefaultGroovyMethods.getAt in the default whitelist, which are inherently unsafe operations that allow direct manipulation of object properties and retrieval of values. These methods enable attackers to circumvent access restrictions by using bracket notation syntax such as currentBuild['rawBuild'] instead of the more restricted dot notation currentBuild.rawBuild. This bypass mechanism operates at the core of the sandbox security model, allowing unauthorized access to build information and system resources that should remain protected. The vulnerability maps directly to CWE-284 Access Control Bypass, as it enables unauthorized access to protected resources through flawed permission controls.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to access private data through the inclusion of groovy.json.JsonOutput.toJson(Closure) and groovy.json.JsonOutput.toJson(Object) in the whitelist. This particular entry allows attackers to serialize closure objects into JSON format, potentially exposing sensitive information that would normally be inaccessible due to script security restrictions. The ability to serialize closure objects provides attackers with a means to extract internal state information, configuration details, and potentially sensitive data that could be used for further exploitation or lateral movement within the system. This vulnerability affects Jenkins and other systems that rely on Groovy sandbox implementations for security, creating a significant risk for continuous integration and deployment environments.
The security implications of CVE-2017-1000095 align with several tactics described in the MITRE ATT&CK framework, particularly those related to privilege escalation and credential access. Attackers can leverage this vulnerability to move laterally within systems by accessing private build information and configuration data that would otherwise be protected. The vulnerability also supports techniques for information gathering and reconnaissance, as the exposed data could include sensitive build artifacts, environment variables, and system configurations. Organizations using affected systems should immediately implement mitigations including updating to patched versions of the vulnerable software, reviewing and tightening whitelist configurations, and implementing additional access controls to limit the impact of potential exploitation.
Mitigation strategies should focus on removing the unsafe entries from the default whitelist configuration and implementing more restrictive access controls for script execution environments. The recommended approach includes updating to patched versions of affected software that properly configure the whitelist to exclude dangerous methods, implementing additional validation layers for script execution, and conducting comprehensive security reviews of all script sandbox configurations. Organizations should also consider implementing network segmentation and monitoring for suspicious script execution patterns that might indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper sandbox configuration and the potential consequences of including overly permissive entries in security-critical components.