CVE-2026-0750: Drupal Commerce Paybox Auth Bypass Flaw

CVE-2026-0750 Overview

CVE-2026-0750 is an Improper Verification of Cryptographic Signature vulnerability affecting the Drupal Commerce Paybox module on Drupal 7.X. This security flaw allows attackers to bypass authentication mechanisms, potentially enabling unauthorized payment transactions and compromising e-commerce integrity.

Critical Impact

This authentication bypass vulnerability in the Commerce Paybox payment module could allow attackers to manipulate payment verification processes, potentially leading to fraudulent transactions and financial loss for e-commerce sites.

Affected Products

• Drupal Commerce Paybox versions 7.x-1.0 through 7.x-1.5
• Drupal 7.X installations using Commerce Paybox module
• E-commerce sites utilizing Paybox payment gateway integration

Discovery Timeline

• 2026-01-28 - CVE-2026-0750 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-0750

Vulnerability Analysis

This vulnerability stems from improper verification of cryptographic signatures in the Drupal Commerce Paybox module (CWE-347). The affected module fails to properly validate the cryptographic signatures used to authenticate payment responses from the Paybox payment gateway. When a payment gateway returns a response to the Drupal e-commerce site, the module should verify that the response has not been tampered with by checking its cryptographic signature. The flaw in signature verification allows attackers to forge or modify payment responses, effectively bypassing the authentication mechanism that ensures payment integrity.

The network-accessible nature of this vulnerability means attackers can exploit it remotely without requiring any user interaction or prior authentication. This makes it particularly dangerous for public-facing e-commerce websites that rely on the Paybox payment integration for processing customer transactions.

Root Cause

The root cause of this vulnerability lies in the inadequate implementation of cryptographic signature verification within the Commerce Paybox module. The module does not properly validate the HMAC signatures or other cryptographic tokens returned by the Paybox payment gateway, allowing forged payment confirmations to be accepted as legitimate. This failure to enforce cryptographic integrity checks violates fundamental secure payment processing principles and enables authentication bypass attacks.

Attack Vector

An attacker can exploit this vulnerability by intercepting or crafting malicious payment gateway responses and submitting them to the vulnerable Drupal site. Since the cryptographic signature verification is flawed, the attacker can modify payment status indicators, transaction amounts, or other critical payment data without detection. The attack can be conducted over the network without requiring any privileges or user interaction, making it accessible to remote attackers targeting e-commerce sites.

The exploitation scenario typically involves the attacker manipulating the callback URL that receives payment confirmation from Paybox, injecting forged response data that indicates successful payment when no actual payment occurred, or modifying transaction amounts after the fact.

Detection Methods for CVE-2026-0750

Indicators of Compromise

• Unexpected or anomalous payment confirmations that don't match gateway transaction logs
• Discrepancies between recorded payments in Drupal and actual Paybox gateway records
• Unusual patterns in payment callback requests, particularly from non-Paybox IP addresses
• Modified or missing cryptographic signature parameters in payment response logs

Detection Strategies

• Cross-reference all Commerce Paybox payment confirmations with actual Paybox gateway transaction records
• Monitor web application logs for payment callback requests with malformed or missing signature parameters
• Implement network monitoring to detect payment callbacks originating from unexpected sources
• Deploy web application firewall (WAF) rules to inspect payment callback traffic for anomalies

Monitoring Recommendations

• Enable detailed logging for all Commerce Paybox module payment processing activities
• Set up alerts for payment confirmation events that lack valid cryptographic signatures
• Monitor for unusual spikes in successful payment confirmations that may indicate exploitation
• Regularly audit payment reconciliation reports to identify discrepancies early

How to Mitigate CVE-2026-0750

Immediate Actions Required

• Audit all recent transactions processed through Commerce Paybox for potential fraudulent activity
• Consider temporarily disabling the Commerce Paybox payment gateway until patched
• Implement additional server-side validation of payment transactions with direct Paybox API verification
• Review access logs for the payment callback endpoints for suspicious activity

Patch Information

Organizations using the affected Drupal Commerce Paybox module versions (7.x-1.0 through 7.x-1.5) should immediately consult the Tag1 Security Advisory for official patch information and remediation guidance. Additional vulnerability details are available at the HeroDev vulnerability directory.

Given that Drupal 7 has reached end-of-life, organizations should strongly consider migrating to supported Drupal versions or utilizing extended support services that provide security updates for legacy installations.

Workarounds

• Implement server-side verification that independently confirms payment status directly with Paybox API before fulfilling orders
• Add IP allowlisting to restrict payment callback acceptance to known Paybox gateway IP addresses only
• Deploy a web application firewall with rules to validate cryptographic parameters in payment callbacks
• Consider using an alternative payment gateway module until a patched version is available

# Example: Restrict payment callback endpoint access by IP in Apache
# Add to .htaccess or Apache configuration
<Location "/commerce-paybox/callback">
    Require ip 195.101.99.0/24
</Location>