CVE-2020-1955 in CouchDB
Summary
by MITRE
CouchDB version 3.0.0 shipped with a new configuration setting that governs access control to the entire database server called `require_valid_user_except_for_up`. It was meant as an extension to the long standing setting `require_valid_user`, which in turn requires that any and all requests to CouchDB will have to be made with valid credentials, effectively forbidding any anonymous requests. The new `require_valid_user_except_for_up` is an off-by-default setting that was meant to allow requiring valid credentials for all endpoints except for the `/_up` endpoint. However, the implementation of this made an error that lead to not enforcing credentials on any endpoint, when enabled. CouchDB versions 3.0.1[1] and 3.1.0[2] fix this issue.
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Analysis
by VulDB Data Team • 05/21/2020
The vulnerability described in CVE-2020-1955 represents a critical access control flaw in Apache CouchDB versions 3.0.0 through 3.0.0, where a misconfiguration in the authentication enforcement mechanism created an unintended security bypass. This issue stems from the implementation of a new configuration parameter called `require_valid_user_except_for_up` which was designed to extend the existing `require_valid_user` setting. The original `require_valid_user` configuration has long been used to mandate valid credentials for all database interactions, effectively blocking anonymous access to the entire CouchDB server. The new parameter was intended to create an exception to this rule by allowing anonymous access specifically to the `/_up` endpoint, which is typically used for health checks and status monitoring. However, the implementation contained a critical logical error that completely bypassed credential validation across all endpoints when the new setting was enabled, regardless of the intended exception behavior.
The technical flaw in this vulnerability manifests as a configuration parsing or enforcement error within CouchDB's access control subsystem, where the conditional logic for applying authentication requirements became inverted or malformed. When administrators enabled the `require_valid_user_except_for_up` setting, the system failed to properly distinguish between the various endpoints and instead applied the same credential-less access policy to all database interactions. This misimplementation violates fundamental security principles of least privilege and defense in depth, as it effectively neutralized the authentication layer that was designed to protect database resources. The vulnerability falls under CWE-284 Access Control Bypass, which specifically addresses situations where access control mechanisms are improperly implemented, allowing unauthorized access to protected resources. The flaw represents a classic example of a security feature being introduced with incorrect implementation logic, creating an unintended backdoor that undermines the entire security posture of the system.
The operational impact of this vulnerability is severe and far-reaching, as it allows any unauthenticated user to access and potentially manipulate database resources that should require valid credentials. Attackers could exploit this flaw to perform unauthorized database operations including but not limited to data reading, writing, modification, and deletion, depending on the permissions assigned to the anonymous user context. The vulnerability particularly affects organizations that rely on CouchDB for data storage and may have configured the new setting in an attempt to provide health monitoring capabilities while maintaining security for other operations. When this setting is enabled, it creates a false sense of security where administrators believe they are maintaining strict access controls, while in reality the entire database server becomes accessible to anyone who can reach the CouchDB endpoints. This vulnerability directly maps to ATT&CK technique T1078 Valid Accounts, as it allows adversaries to gain access to systems using valid but potentially misconfigured accounts, and T1566 Phishing for Information, as it could be exploited to gain unauthorized access to sensitive data that organizations believe is protected.
Organizations affected by this vulnerability should immediately upgrade to CouchDB versions 3.0.1 or 3.1.0, which contain the necessary patches to correct the access control implementation. Administrators should also review their current configuration files to ensure that the `require_valid_user_except_for_up` setting is either disabled or properly configured if needed, and that the `require_valid_user` setting is appropriately enforced for all database operations. Security monitoring should be enhanced to detect any unusual access patterns that might indicate exploitation attempts, particularly around database endpoints that should normally require authentication. The vulnerability highlights the importance of thorough testing of security-related configuration changes and the need for comprehensive security reviews of new features before deployment in production environments. Organizations should also implement proper access control monitoring and audit logging to detect potential unauthorized access attempts, ensuring that all database interactions are properly authenticated and authorized according to established security policies.