CVE-2026-16642: Drupal Email Login OTP Auth Bypass Flaw

CVE-2026-16642 Overview

CVE-2026-16642 is an input validation vulnerability [CWE-20] in the Drupal Email Login OTP contributed module. The module provides one-time password (OTP) email-based authentication for Drupal sites. The flaw stems from improper input validation in the module's authentication workflow.

Exploitation requires network access, high attacker privileges, and user interaction. Attack complexity is high, which limits the practical exploitability of the issue. Successful exploitation can compromise the confidentiality and integrity of affected Drupal installations.

Critical Impact
An authenticated attacker with elevated privileges can leverage improper input validation in the Email Login OTP module to affect confidentiality and integrity on Drupal sites that install the module.

Affected Products

Drupal Email Login OTP contributed module
Drupal sites with the Email Login OTP module installed and enabled
Refer to the Drupal Security Advisory for exact version boundaries

Discovery Timeline

2026-08-25 - CVE-2026-16642 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-16642

Vulnerability Analysis

The vulnerability resides in the Drupal Email Login OTP module, which authenticates users through one-time passwords delivered by email. Drupal categorizes the issue under [CWE-20] Improper Input Validation. The module fails to sufficiently validate input handled during the OTP authentication flow.

An attacker must already hold elevated privileges within the Drupal site and must convince a legitimate user to perform an action. These preconditions raise the exploitation barrier. However, when preconditions are met, the attacker can influence data confidentiality and integrity within the affected site.

The EPSS score for this vulnerability is low, reflecting limited likelihood of widespread exploitation in the near term. No public proof-of-concept exploit is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The root cause is improper input validation within the Email Login OTP authentication logic. Input processed during the OTP workflow is not adequately verified against expected constraints. This gap allows an attacker with the required privileges to submit values that alter authentication behavior or expose protected data.

Attack Vector

The attack vector is network-based. An attacker interacts with the Drupal site through standard HTTP or HTTPS requests. Successful exploitation requires an authenticated session with high privileges and user interaction with an attacker-supplied action or link. No verified public code example exists; consult the Drupal Security Advisory for specific technical details and vendor-confirmed exploitation preconditions.

Detection Methods for CVE-2026-16642

Indicators of Compromise

Unexpected successful OTP authentication events for accounts that did not initiate a login
Drupal watchdog or dblog entries showing repeated OTP requests from privileged accounts
Anomalous session creation events tied to the Email Login OTP module workflow
Modification of user records or content immediately following an OTP login sequence

Detection Strategies

Audit Drupal user and watchdog tables for OTP-related authentication events correlated with privileged account activity
Enable verbose logging on the Email Login OTP module and forward logs to a centralized SIEM for correlation
Compare Email Login OTP module version against the fixed version listed in the vendor advisory across all Drupal installations

Monitoring Recommendations

Monitor administrative account activity for atypical OTP login patterns, including off-hours access and geographic anomalies
Alert on configuration changes to the Email Login OTP module, including permission grants and settings modifications
Track HTTP requests to OTP authentication endpoints and flag repeated submissions or malformed payloads

How to Mitigate CVE-2026-16642

Immediate Actions Required

Review the Drupal Security Advisory and identify affected Email Login OTP module versions in your environment
Update the Email Login OTP module to the fixed release identified in the advisory
Audit privileged Drupal accounts and revoke unnecessary administrative permissions to reduce exploitation preconditions
Rotate credentials for any accounts that show suspicious OTP authentication activity

Patch Information

Drupal has published guidance in the contributed module security advisory sa-contrib-2026-085. Apply the module update through Drupal's standard update workflow using Composer or the administrative update interface. Verify the module version after upgrade with drush pm:list --status=enabled or the Extend page in the Drupal admin UI.

Workarounds

Disable the Email Login OTP module until the patched version is deployed if the update cannot be applied immediately
Restrict access to Drupal administrative endpoints using web application firewall rules or IP allowlisting
Enforce multi-factor authentication for privileged accounts using an alternative, unaffected authentication provider

bash

# Update the Email Login OTP module via Composer and clear caches
composer update drupal/email_login_otp --with-dependencies
drush updatedb -y
drush cache:rebuild
drush pm:list --status=enabled | grep email_login_otp