CVE-2020-11980 in Karaf
Summary
by MITRE
In Karaf, JMX authentication takes place using JAAS and authorization takes place using ACL files. By default, only an "admin" can actually invoke on an MBean. However there is a vulnerability there for someone who is not an admin, but has a "viewer" role. In the 'etc/jmx.acl.cfg', such as role can call get*. It's possible to authenticate as a viewer role + invokes on the MLet getMBeansFromURL method, which goes off to a remote server to fetch the desired MBean, which is then registered in Karaf. At this point the attack fails as "viewer" doesn't have the permission to invoke on the MBean. Still, it could act as a SSRF style attack and also it essentially allows a "viewer" role to pollute the MBean registry, which is a kind of privilege escalation. The vulnerability is low as it's possible to add a ACL to limit access. Users should update to Apache Karaf 4.2.9 or newer.
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Analysis
by VulDB Data Team • 06/13/2020
The vulnerability described in CVE-2020-11980 resides within the Apache Karaf application server's JMX security implementation, specifically concerning the interaction between authentication mechanisms and access control lists. This flaw demonstrates a critical weakness in the privilege separation model that governs how different user roles interact with the management interface. The vulnerability operates through a sophisticated attack vector that exploits the layered security model where JMX authentication relies on JAAS (Java Authentication and Authorization Service) while authorization is managed through ACL (Access Control List) configuration files. The default security posture restricts MBean invocation to only the admin role, yet this design contains a significant gap that allows users with the viewer role to potentially escalate their privileges.
The technical execution of this vulnerability leverages the MLet MBean functionality, which serves as a mechanism for dynamically loading and registering MBeans from remote URLs. When a user authenticates with the viewer role, they can invoke the getMBeansFromURL method, which acts as a bridge to remote servers and facilitates the retrieval of MBeans that are subsequently registered within the Karaf environment. This process creates a pathway for what security researchers categorize as a Server-Side Request Forgery (SSRF) attack pattern, where the viewer role can effectively make the Karaf server initiate network requests to arbitrary destinations. The attack exploits the fact that while the viewer role cannot directly invoke operations on the remotely retrieved MBeans, they can still influence the MBean registry through the MLet mechanism, thereby polluting the system with potentially malicious or unauthorized MBeans.
This vulnerability represents a privilege escalation scenario that falls under the CWE-269 Improper Privilege Management category, where insufficient access control allows a low-privilege user to gain elevated capabilities within the system. The operational impact extends beyond simple information disclosure or unauthorized access, as the attacker can effectively corrupt the MBean registry with potentially malicious components that may persist within the system. The vulnerability also aligns with ATT&CK technique T1078 Valid Accounts, where an attacker leverages legitimate user accounts with restricted permissions to perform actions that should be restricted. The attack essentially allows a viewer role user to act as a man-in-the-middle, injecting foreign MBeans into the system's management interface, which could potentially be used to further compromise the system or to establish persistence mechanisms.
The security implications of this vulnerability are particularly concerning because it demonstrates how seemingly isolated security controls can interact in unexpected ways to create broader attack surfaces. The fact that the vulnerability can be mitigated through simple ACL configuration updates suggests that the root cause lies in overly permissive default configurations rather than fundamental architectural flaws. However, this also means that organizations relying on default Karaf installations may be unknowingly exposed to this attack vector. The recommended mitigation of updating to Apache Karaf 4.2.9 or newer addresses the core issue by implementing stricter access controls around the MLet functionality and ensuring that the viewer role cannot influence the MBean registry through remote MBean loading operations. This vulnerability highlights the importance of proper privilege separation in management interfaces and demonstrates how even seemingly minor access control gaps can lead to significant security implications in enterprise application servers.