CVE-2025-31691 in OAuth2 Server
Summary
by MITRE • 04/01/2025
Missing Authorization vulnerability in Drupal OAuth2 Server allows Forceful Browsing.This issue affects OAuth2 Server: from 0.0.0 before 2.1.0.
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Analysis
by VulDB Data Team • 09/02/2025
The CVE-2025-31691 vulnerability represents a critical authorization flaw within the Drupal OAuth2 Server module that exposes systems to unauthorized access through forceful browsing techniques. This vulnerability specifically impacts versions prior to 2.1.0, creating a significant security gap where authenticated users can potentially bypass intended access controls and gain unauthorized access to protected resources. The issue stems from inadequate validation of user permissions and session states during OAuth2 token exchanges and resource access requests.
This missing authorization vulnerability operates by exploiting the absence of proper access control checks within the OAuth2 server implementation. When users attempt to access protected resources through forceful browsing methods, the system fails to verify whether the requesting entity has legitimate authorization to access the specific resource. The flaw allows attackers to manipulate request parameters and bypass the normal authorization flow that should occur during OAuth2 token validation. This creates an environment where unauthorized access can occur even when proper authentication has been established, fundamentally undermining the security model of the OAuth2 implementation.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential data breaches, privilege escalation, and system compromise. Attackers can leverage this weakness to access sensitive user information, manipulate protected resources, and potentially escalate their privileges within the Drupal environment. The vulnerability particularly affects organizations relying on OAuth2 for authentication and authorization, as it undermines the trust model that OAuth2 is designed to provide. Systems utilizing the affected Drupal OAuth2 Server module become vulnerable to attacks that can result in unauthorized data exposure, session hijacking, and potential lateral movement within the network infrastructure.
Security practitioners should immediately implement mitigations including upgrading to version 2.1.0 or later of the Drupal OAuth2 Server module to address the missing authorization controls. Additionally, organizations should review their existing OAuth2 configurations and implement additional access control measures such as rate limiting, enhanced logging, and monitoring for anomalous access patterns. The vulnerability aligns with CWE-862 which specifically addresses "Missing Authorization" flaws in software systems, and represents a clear violation of the principle of least privilege. From an ATT&CK perspective, this vulnerability maps to techniques involving privilege escalation and unauthorized access to resources, potentially enabling adversaries to move laterally within the system and access sensitive information that should remain protected through proper authorization controls. Organizations should also consider implementing network segmentation and additional authentication layers to reduce the impact of such authorization failures.