CVE-2018-15728 in Couchbase Server
Summary
by MITRE
An issue was discovered in Couchbase Server. Authenticated users can send arbitrary Erlang code to the 'diag/eval' endpoint of the REST API (available by default on TCP/8091 and/or TCP/18091). The executed code in the underlying operating system will run with the privileges of the user running Couchbase server.
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Analysis
by VulDB Data Team • 03/18/2020
This vulnerability exists within Couchbase Server's REST API implementation where authenticated users can exploit a code execution flaw through the diag/eval endpoint. The issue stems from insufficient input validation and sanitization mechanisms that allow maliciously crafted Erlang code to be passed directly to the evaluation engine. This represents a critical privilege escalation vulnerability as the executed code operates with the same privileges as the Couchbase server process, potentially compromising the entire database infrastructure. The vulnerability affects the default configuration where the REST API listens on TCP ports 8091 and 18091, making it accessible to any authenticated user who can establish a connection to these endpoints.
The technical exploitation of this vulnerability involves sending specially crafted Erlang code through the diag/eval REST endpoint, which then gets evaluated by the underlying Erlang runtime environment. Since Couchbase server typically runs with elevated privileges to manage database operations, any code executed through this vector inherits those privileges. This creates a scenario where an authenticated attacker can execute arbitrary commands on the host system, potentially leading to complete system compromise. The vulnerability is particularly dangerous because it bypasses normal access controls and operates at the operating system level, allowing attackers to perform actions such as file system manipulation, process execution, and network reconnaissance.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise and data exfiltration capabilities. Attackers can leverage this vulnerability to establish persistent access, escalate privileges further, and move laterally within the network infrastructure. The default exposure of the affected ports without additional security controls means that organizations with standard Couchbase deployments are immediately at risk. This vulnerability directly maps to CWE-94 - Improper Control of Generation of Code ('Code Injection') and aligns with ATT&CK technique T1059.006 - Command and Scripting Interpreter: Erlang, demonstrating how attackers can leverage legitimate system tools for malicious purposes. Organizations using Couchbase Server without proper network segmentation or additional authentication layers face severe consequences including data breaches, service disruption, and regulatory compliance violations.
Mitigation strategies should focus on immediate network-level controls and configuration hardening measures. Organizations should implement strict firewall rules to restrict access to TCP ports 8091 and 18091 to trusted networks only, effectively limiting exposure to authenticated users within the organization. Additionally, disabling the diag/eval endpoint through configuration changes or applying the vendor-provided security patches is essential. Network monitoring should be enhanced to detect unusual API access patterns and code execution attempts. Regular security assessments should include testing for similar vulnerabilities in other database systems and web applications. The implementation of principle of least privilege should be enforced where Couchbase server runs with minimal required permissions, and regular audits should verify that no unnecessary services are exposed to untrusted networks. Organizations should also consider implementing intrusion detection systems specifically tuned to detect exploitation attempts targeting this type of code execution vulnerability.