CVE-2026-6816: Drupal TFA Basic Plugins Access Control Bypass

Technical summary

CVE-2026-6816 is an improper access control vulnerability (CWE-267) in Drupal TFA Basic Plugins affecting versions 7.x-1.0 through 7.x-1.2. The module fails to enforce granular permission checks when handling two-factor authentication recovery codes. A user holding the 'administer users' permission can programmatically view or generate recovery codes for any other user account, circumventing intended authorization boundaries. The vulnerability is accessed over the network without requiring user interaction and operates at the application logic layer where permission inheritance is not properly validated.

Business impact

This vulnerability creates a lateral privilege escalation risk in multi-administrator environments and erodes trust in two-factor authentication recovery workflows. An administrator with limited scope—such as a user support role holding only 'administer users'—could unlock other user accounts, including those with higher privileges. In regulated environments, unauthorized access to or modification of authentication recovery data may trigger compliance violations. The low CVSS score reflects that exploitation requires existing administrative access, but the impact on authentication integrity is meaningful and should not be dismissed.

Affected systems

Only Drupal TFA Basic Plugins project versions 7.x-1.0, 7.x-1.1, and 7.x-1.2 are affected. Organizations running Drupal with the TFA Basic Plugins module should verify their installed version. Verify against the vendor advisory to confirm which patch versions address this issue. The vulnerability does not affect Drupal core or other TFA implementations; only this specific contributed module is impacted.

Exploitability

Exploitation requires an authenticated account with 'administer users' permission, making this a high-privilege attack with a low barrier once that privilege level is obtained. No external enumeration, social engineering, or public-facing exploits are required; a simple API or administrative interface query can retrieve or regenerate codes. The attack is deterministic and leaves limited forensic evidence in typical logging configurations. However, the prerequisite of administrative access significantly limits opportunistic exploitation in well-segmented environments.

Remediation

Update Drupal TFA Basic Plugins to a patched version released after 7.x-1.2. Verify the specific patched version against the vendor advisory before deployment. Organizations should also audit recent administrative activity related to recovery code generation or access to identify potential unauthorized use. Review 'administer users' role assignments and apply least-privilege principles to scope that permission narrowly.

Patch guidance

Obtain the latest stable release of TFA Basic Plugins from the Drupal project repository and apply it through Drupal's update mechanism. Test the patch in a staging environment before production deployment to ensure compatibility with your Drupal version and other installed modules. Verify against the official Drupal security advisory to confirm the exact patched version number and any additional configuration changes required.

Detection guidance

Monitor for administrative API calls or web requests that access recovery code endpoints or permissions checks related to two-factor authentication settings. Alert on any instances where a user with 'administer users' permission accesses recovery code data for accounts other than their own. Review audit logs for unusual patterns in user account modifications or permission escalations. If possible, log all calls to TFA recovery code generation or retrieval functions along with the requesting user's identity.

Why prioritize this

Although the CVSS score is low, the integrity of two-factor authentication recovery—a critical backup authentication mechanism—is compromised. Organizations should prioritize patching in environments where admin roles are distributed across multiple users, where insider threat is a concern, or where regulatory requirements mandate strong separation of duties. Conversely, organizations with centralized, tightly controlled admin access may defer this lower in the queue, provided monitoring for suspicious activity is in place.

Risk score, explained

The CVSS 3.1 score of 3.8 reflects a low severity due to the requirement for high-level privileges (PR:H), lack of user interaction (UI:N), and limited scope (S:U). However, the confidentiality and integrity impact (C:L, I:L) is non-zero because recovery codes can be exposed or overwritten. The low score should not be mistaken for 'no risk'—the vulnerability specifically weakens a critical security function that users depend on when locked out of their primary authentication factor.

Frequently asked questions