Parse Server is an open-source backend framework that runs on Node.js and commonly uses MongoDB as its database. The MongoDB explain() method provides detailed insights into query execution plans, including index usage, collection scanning, and performance metrics. Prior to version 8.5.0-alpha.5, parse-server allowed any client to execute explain queries without requiring the master key or any authentication. This means that an unauthenticated attacker can retrieve sensitive information about the database schema, such as field names, index configurations, and query optimization details. Such information leakage can assist attackers in identifying potential attack vectors, including performance exploitation or crafting more effective queries to extract or manipulate data. The vulnerability is classified under CWE-201 (Insertion of Sensitive Information Into Sent Data), indicating that sensitive internal data is exposed in responses to unauthorized clients. To address this, version 8.5.0-alpha.5 introduced a configuration option databaseOptions.allowPublicExplain, which when set to false restricts explain queries to requests authenticated with the master key. However, to maintain backward compatibility, this option currently defaults to true, allowing public explain queries and logging a security warning if not explicitly set. The default is planned to change to false in a future major release, enhancing security by default. Until then, organizations are recommended to implement custom middleware to block explain queries from non-master-key requests or monitor and alert on explain query usage to detect potential abuse. The CVSS 4.0 vector indicates the vulnerability is remotely exploitable over the network without authentication or user interaction, with low attack complexity and no impact on confidentiality, integrity, or availability directly, but with significant information disclosure risk.

For European organizations using parse-server versions prior to 8.5.0-alpha.5, this vulnerability poses a risk of sensitive database schema and performance information disclosure. Attackers gaining such insights can better understand the database structure, enabling them to craft more precise and efficient attacks, such as targeted data extraction, privilege escalation, or denial-of-service via query performance exploitation. While the vulnerability does not directly compromise data confidentiality or integrity, the leaked information significantly lowers the barrier for subsequent attacks. This is particularly critical for organizations handling sensitive or regulated data, such as financial institutions, healthcare providers, or government agencies in Europe. Exposure of index and query plan details can also aid attackers in identifying inefficient queries or bottlenecks to degrade service availability. The vulnerability's network-exploitable nature without authentication increases the attack surface, especially for publicly accessible parse-server deployments. Consequently, European organizations face increased risk of reconnaissance and follow-on attacks that could lead to data breaches or service disruptions if not mitigated promptly.

European organizations should take the following specific actions to mitigate this vulnerability: 1) Upgrade parse-server to version 8.5.0-alpha.5 or later where the databaseOptions.allowPublicExplain configuration option is available. 2) Explicitly set databaseOptions.allowPublicExplain to false in configuration to restrict explain queries to master key authenticated requests, even if this may require testing for compatibility. 3) If immediate upgrade is not feasible, implement custom middleware to intercept and block explain queries from requests lacking the master key, ensuring no unauthorized explain queries are processed. 4) Enable detailed logging and monitoring of all explain query usage to detect and alert on suspicious or unexpected explain query activity. 5) Conduct internal audits of parse-server deployments to identify publicly accessible endpoints that could be exploited. 6) Review and harden access controls around master key distribution and usage to prevent unauthorized access. 7) Prepare for the upcoming major release where the default will change to disallow public explain queries, ensuring compatibility and security posture are maintained. 8) Educate development and operations teams about the risks of exposing database internals and the importance of secure configuration management. These steps go beyond generic advice by focusing on configuration changes, monitoring, and proactive blocking tailored to parse-server's architecture and the specifics of this vulnerability.