CVE-2018-11116 in OpenWrt
Summary
by MITRE
OpenWrt mishandles access control in /etc/config/rpcd and the /usr/share/rpcd/acl.d files, which allows remote authenticated users to call arbitrary methods (i.e., achieve ubus access over HTTP) that were only supposed to be accessible to a specific user, as demonstrated by the file, log, and service namespaces, potentially leading to remote Information Disclosure or Code Execution. NOTE: The developer disputes this as a vulnerability, indicating that rpcd functions appropriately
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2018-11116 resides within the OpenWrt operating system's handling of access control mechanisms in the rpcd service configuration files. This issue manifests in the improper management of access control lists located in /etc/config/rpcd and /usr/share/rpcd/acl.d directories, which are critical components for controlling ubus method access over HTTP. The flaw represents a significant security weakness that undermines the intended authorization model of the system, allowing authenticated users to bypass normal access restrictions and invoke methods that should be restricted to specific user roles.
The technical implementation of this vulnerability stems from how the rpcd service processes access control definitions in its configuration files. When users authenticate to the system, the rpcd service should enforce strict access control policies based on the defined ACL rules in the acl.d directory. However, due to a flaw in the access control parsing or enforcement logic, authenticated users can escalate their privileges to access methods within the file, log, and service namespaces that are typically restricted to administrative or specific user roles. This represents a classic privilege escalation vulnerability where legitimate authenticated access is leveraged to gain unauthorized capabilities.
The operational impact of this vulnerability extends beyond simple access control bypass and can potentially lead to severe consequences including information disclosure and code execution. Remote authenticated attackers can exploit this flaw to access sensitive system information through the file namespace, retrieve system logs via the log namespace, and potentially control system services through the service namespace. These capabilities align with attack patterns described in the ATT&CK framework under privilege escalation and defense evasion techniques. The vulnerability particularly affects systems where rpcd is enabled and configured with default or improperly configured access controls, making it a significant concern for network administrators managing OpenWrt-based devices.
From a CWE perspective, this vulnerability maps to CWE-284: Improper Access Control, which specifically addresses weaknesses in authorization mechanisms. The flaw represents a failure in implementing proper access control checks within the rpcd service, allowing unauthorized method invocation. The attack surface is particularly concerning because it affects core system services that are essential for device management and monitoring. The developer's assertion that this is not a vulnerability may stem from their perspective on intended system behavior, but from a security standpoint, the unauthorized access to restricted namespaces clearly violates proper security boundaries and authorization principles. Organizations should implement mitigations including strict configuration of access control lists, regular auditing of rpcd configurations, and network segmentation to limit exposure of affected systems. The vulnerability underscores the critical importance of proper access control implementation in embedded systems where administrative interfaces are exposed to network access.
This vulnerability demonstrates the complexity of access control implementations in embedded operating systems and highlights the need for thorough security testing of system services. The rpcd service's failure to properly enforce access controls creates a pathway for attackers to escalate privileges and access sensitive system resources. The impact is particularly severe because it affects fundamental system management capabilities, potentially allowing attackers to compromise entire networks of OpenWrt devices. The issue serves as a reminder that even well-established systems require continuous security assessment and proper configuration management to prevent unauthorized access to critical system functions.