CVE-2026-16639 in Internationalization Single Sign-On Plugin
Summary
by MITRE • 08/26/2026
Authentication Bypass Using an Alternate Path or Channel vulnerability in Drupal Internationalization Single Sign-On allows Authentication Bypass. This issue affects Internationalization Single Sign-On versions: from 0.0.0 to 1.8.0.
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Analysis
by VulDB Data Team • 08/26/2026
The identified security flaw resides within the Drupal Internationalization Single Sign-On module, specifically affecting version ranges from 0.0.0 through 1.8.0. This vulnerability is classified as an Authentication Bypass Using an Alternate Path or Channel, which corresponds to CWE-287 in the Common Weakness Enumeration taxonomy. The core technical issue stems from a failure in the authentication logic where the module fails to properly enforce access controls across all entry points for user identity verification. In typical web application architectures, authentication mechanisms are expected to be uniformly applied regardless of how a request reaches the server. However, in this specific implementation, there exists an alternative code path or channel through which requests can bypass the standard credential validation routines. This architectural oversight allows attackers who possess knowledge of these alternate paths to interact with protected resources without providing valid credentials, effectively circumventing the intended security boundaries established by the application developers.
From a technical perspective, such vulnerabilities often arise when developers implement custom authentication handlers or API endpoints that do not inherit the same security checks as the primary login forms. In the context of Drupal modules dealing with internationalization and single sign-on integration, there may be specific hooks or callback functions designed to handle token-based authentication or federated identity assertions. If these callbacks are configured to trust incoming data without rigorous validation against a central authority or if they fail to check session state integrity before granting access, an attacker can exploit this gap. By crafting requests that target these less scrutinized pathways, the malicious actor can inject forged tokens or manipulate parameters in a way that tricks the application into believing the user is authenticated. This bypass does not require breaking encryption algorithms or exploiting buffer overflows but rather exploits logical flaws in how trust is established and maintained across different components of the system.
The operational impact of this vulnerability is severe, as it directly compromises the confidentiality and integrity of sensitive data protected by authentication controls. An attacker who successfully exploits this alternate path can gain unauthorized access to administrative interfaces, user profiles, or private content within the Drupal site. This level of access enables a wide range of malicious activities including data exfiltration, modification of critical system configurations, installation of persistent backdoors, and further lateral movement within the network if the compromised account has elevated privileges. Since single sign-on modules often serve as gateways to multiple integrated services or internal tools, compromising this entry point can lead to broader systemic compromise beyond just the Drupal instance itself. The ability to bypass authentication entirely undermines the fundamental security principle of least privilege and renders other defensive measures such as firewalls or intrusion detection systems less effective if they rely on identifying authenticated user behavior patterns.
To mitigate this risk, immediate action is required by upgrading the Internationalization Single Sign-On module to a version newer than 1.8.0 where these logical flaws have been addressed in subsequent releases. Developers and system administrators should verify that all authentication endpoints enforce consistent validation logic regardless of the request method or channel used. It is also advisable to implement defense-in-depth strategies such as multi-factor authentication for administrative accounts, which would add an additional layer of verification even if a single credential-based bypass occurs. Furthermore, conducting regular code audits focused on access control lists and session management can help identify similar architectural weaknesses in other parts of the application. Monitoring logs for unusual authentication patterns or requests to non-standard endpoints may also aid in early detection of exploitation attempts while patches are being deployed. This vulnerability highlights the critical importance of ensuring that security controls are applied holistically across all system interfaces rather than relying on isolated checks within specific modules.