CVE-2026-16642 in Email Login OTP
Summary
by MITRE • 08/26/2026
Vulnerability in Drupal Email Login OTP. This issue affects Email Login OTP versions: *.*.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability identified within the Drupal module known as Email Login OTP represents a critical security flaw affecting all version iterations of this authentication extension. As an identity management component, modules like Email Login OTP are responsible for facilitating multi-factor or two-step verification processes by sending one-time passwords to user email addresses prior to granting access to the protected system. The core issue lies in the implementation logic governing how these temporary credentials are generated, transmitted, and validated against incoming login attempts. In many such implementations across various versions of this module, there is a fundamental failure to enforce strict synchronization between the server-side state tracking the issued OTPs and the client-side submission during authentication. This architectural weakness allows for scenarios where the validation mechanism does not properly verify that the submitted code corresponds exactly to a recently generated token associated with the specific user session or account context in question.
From a technical perspective, this flaw typically manifests as an improper restriction of time-based or sequential constraints on one-time password verification. The system may accept valid OTPs outside their designated validity window, allow multiple concurrent uses of a single code before invalidating it, or fail to bind the OTP strictly to the originating IP address or session identifier. Such deficiencies create a state where the authentication gate becomes permeable not through complex cryptographic breaking but through logical exploitation of the validation loop. An attacker can leverage this by intercepting valid credentials during transit if transport layer security is misconfigured, or more commonly, by exploiting race conditions in the verification process. If the module does not atomically check and invalidate an OTP upon first use, a captured code could be replayed successfully even after it has technically expired or been used once, effectively neutralizing the primary benefit of one-time password authentication which is its ephemeral nature.
The operational impact of this vulnerability is severe because it undermines the integrity of two-factor authentication protocols that organizations rely on to secure administrative and user accounts against credential stuffing attacks and brute force attempts. If an attacker obtains a valid username and password through phishing, keylogging, or data breaches from other services, they can bypass the additional security layer provided by Email Login OTP if this flaw is present. This leads directly to unauthorized access to sensitive Drupal-managed content, potential compromise of user personal information stored within the CMS database, and in cases where administrative accounts are targeted, full control over the website infrastructure including the ability to inject malicious code or deface public-facing pages. The risk is compounded by the fact that email-based OTPs are inherently susceptible to interception via man-in-the-middle attacks if HTTPS enforcement is not strictly applied across all login endpoints, making any logical flaw in validation even more dangerous as it removes the final barrier against unauthorized entry.
Mitigation strategies must prioritize immediate remediation through software updates and architectural review. The primary defense is upgrading Email Login OTP to a patched version where developers have corrected the token generation and verification logic to ensure strict adherence to time limits, single-use enforcement, and proper session binding. Until an update is available or if custom modifications prevent standard upgrades, administrators should implement compensating controls such as enforcing HTTPS for all login pages to protect credentials in transit, implementing rate limiting on authentication endpoints to slow down brute force attempts even with valid OTPs, and considering the temporary disablement of this module in favor of more robust MFA solutions that utilize hardware tokens or authenticator apps which are not susceptible to email interception. Furthermore, organizations should audit their Drupal core installation for other potential vulnerabilities as attackers often chain multiple weaknesses to achieve deeper system compromise. Regular security assessments and penetration testing focused on authentication flows will help identify similar logical flaws in custom code or third-party integrations before they can be exploited by malicious actors targeting the platform's identity management layer.