CVE-2026-3214: Drupal CAPTCHA Auth Bypass Vulnerability

CVE-2026-3214 Overview

CVE-2026-3214 is an authentication bypass vulnerability affecting the Drupal CAPTCHA contributed module. The flaw, classified under CWE-288, allows attackers to bypass CAPTCHA functionality through an alternate path or channel. Affected versions include CAPTCHA from 0.0.0 before 1.17.0 and from 2.0.0 before 2.0.10. The vulnerability is exploitable over the network without authentication or user interaction, enabling attackers to defeat the human verification controls that protect Drupal forms from automated abuse.

Critical Impact

Remote attackers can bypass CAPTCHA verification on protected Drupal forms, enabling automated submissions, credential stuffing, spam, and abuse of any workflow relying on CAPTCHA for bot prevention.

Affected Products

• Drupal CAPTCHA module versions 0.0.0 through 1.16.x (fixed in 1.17.0)
• Drupal CAPTCHA module versions 2.0.0 through 2.0.9 (fixed in 2.0.10)
• Drupal sites using the contributed CAPTCHA module for form protection

Discovery Timeline

• 2026-03-25 - CVE-2026-3214 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-3214

Vulnerability Analysis

The vulnerability is an authentication bypass using an alternate path or channel ([CWE-288]). The Drupal CAPTCHA module enforces a human verification challenge before processing form submissions. An attacker can reach a form-processing code path that does not invoke the CAPTCHA validation step, allowing the submission to proceed as if the challenge had been solved.

The issue affects confidentiality and integrity at a limited scope but does not directly compromise availability. The practical risk depends on which forms a site protects with CAPTCHA. Common targets include login forms, registration forms, password reset workflows, contact forms, and comment submissions.

Root Cause

The root cause is an incomplete enforcement of the CAPTCHA validation control across all entry points that handle protected form submissions. One or more alternate code paths process form data without first verifying the CAPTCHA response token. The fix in versions 1.17.0 and 2.0.10 closes this gap by ensuring CAPTCHA validation is enforced on every path that handles protected submissions.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker crafts HTTP requests targeting the alternate processing path on a Drupal site running a vulnerable CAPTCHA module. The request omits or manipulates the CAPTCHA token while still triggering the underlying form action. Because validation is not enforced on this path, the server processes the submission. Refer to the Drupal Security Advisory for technical specifics.

Detection Methods for CVE-2026-3214

Indicators of Compromise

• Spikes in successful form submissions without corresponding CAPTCHA challenge requests in web server logs
• High-volume POST requests to form endpoints from a small set of source IPs or user agents
• Surges in new user registrations, comments, or contact submissions outside normal baselines
• Authentication or password-reset attempts arriving without preceding CAPTCHA asset loads such as image, audio, or JavaScript challenges

Detection Strategies

• Inventory all Drupal sites and identify installations of the CAPTCHA contributed module with version below 1.17.0 or below 2.0.10
• Correlate form submission events with CAPTCHA validation events in application logs to detect submissions that skipped validation
• Deploy WAF or reverse-proxy rules that flag form POSTs missing expected CAPTCHA token parameters

Monitoring Recommendations

• Enable verbose logging on the CAPTCHA module and forward logs to a central SIEM or data lake for analysis
• Alert on rate anomalies for sensitive endpoints such as /user/login, /user/register, and /user/password
• Track failed login and account creation rates per source IP and per user agent to identify automation

How to Mitigate CVE-2026-3214

Immediate Actions Required

• Upgrade the Drupal CAPTCHA module to version 1.17.0 for 1.x branch deployments
• Upgrade the Drupal CAPTCHA module to version 2.0.10 for 2.x branch deployments
• Audit recent form submissions on protected endpoints for signs of automated abuse since the affected versions were deployed
• Reset credentials and review accounts created during the exposure window if abuse is suspected

Patch Information

The Drupal security team released fixed versions 1.17.0 and 2.0.10 of the CAPTCHA module. Site administrators should apply the update using Composer or the Drupal admin update workflow. Full details are available in the Drupal Security Advisory SA-CONTRIB-2026-015.

Workarounds

• Apply rate limiting at the web server or WAF layer to throttle requests against form endpoints protected by CAPTCHA
• Temporarily disable affected forms or require authenticated access until the module is updated
• Add an additional bot-mitigation control such as a third-party CAPTCHA service or honeypot field on critical forms

# Update the Drupal CAPTCHA module using Composer
composer update drupal/captcha --with-dependencies

# Clear Drupal caches after the update
drush cache:rebuild

# Verify the installed module version
drush pm:list --type=module --status=enabled | grep captcha