CVE-2017-6924 in Drupal
Summary
by MITRE
In Drupal 8 prior to 8.3.7; When using the REST API, users without the correct permission can post comments via REST that are approved even if the user does not have permission to post approved comments. This issue only affects sites that have the RESTful Web Services (rest) module enabled, the comment entity REST resource enabled, and where an attacker can access a user account on the site with permissions to post comments, or where anonymous users can post comments.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-6924 represents a critical authorization bypass flaw in Drupal 8 versions prior to 8.3.7 that specifically impacts the RESTful Web Services module functionality. This security issue stems from improper access control validation within the comment posting mechanism when utilizing the REST API interface. The flaw allows unauthorized users to submit comments that bypass the normal approval workflow, effectively enabling them to post content that would typically require elevated permissions. The vulnerability is particularly concerning because it operates at the application layer, exploiting the gap between the REST API's permission handling and the traditional content management system's authorization mechanisms.
The technical root cause of this vulnerability lies in the insufficient validation of user permissions during REST API comment creation operations. When the RESTful Web Services module processes comment submissions through its API endpoints, it fails to properly verify whether the submitting user possesses the necessary authorization levels to post comments that are automatically approved. This misconfiguration allows attackers to leverage existing user accounts with basic comment posting permissions or even anonymous access to create comments that bypass the standard moderation queue. The flaw specifically manifests when the comment entity REST resource is enabled, creating an attack surface where the API's permission model does not align with the site's content approval policies.
The operational impact of this vulnerability extends beyond simple content manipulation, potentially enabling attackers to flood sites with spam content or malicious payloads that appear to originate from legitimate users. This authorization bypass can compromise the integrity of comment systems, particularly on sites where comment moderation is crucial for maintaining community standards or preventing abuse. The vulnerability affects organizations that rely on Drupal's REST API for integration with external applications or mobile clients, as these interfaces may inadvertently expose the permission bypass to unauthorized parties. Security implications include potential data integrity issues, reputation damage from spam content, and the possibility of attackers using the compromised comment system as a vector for further attacks within the application ecosystem.
Organizations should implement immediate mitigations including upgrading to Drupal 8.3.7 or later versions where this vulnerability has been patched, disabling the comment entity REST resource when not required, and reviewing existing user permissions to minimize potential attack vectors. The fix addresses the core authorization validation issue by ensuring that REST API comment submissions properly verify user permissions against the site's configured comment approval policies. Additionally, administrators should consider implementing additional monitoring for unusual comment submission patterns and review REST API access controls to prevent unauthorized users from accessing comment-related endpoints. This vulnerability aligns with CWE-285, which addresses improper authorization issues in software systems, and represents a classic example of how API security controls can be bypassed when proper access validation is not implemented across all application interfaces. The ATT&CK framework categorizes this as a privilege escalation technique, where attackers leverage API endpoints to gain elevated access to system functionality that should be restricted to authorized users only.