CVE-2026-84918 in Monobank Payment API
Summary
by MITRE • 10/22/2026
Improper Verification of Cryptographic Signature vulnerability in Drupal Monobank payment API allows Signature Spoof. This issue affects Monobank payment API versions: from 0.0.0 to 1.0.3.
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Analysis
by VulDB Data Team • 10/22/2026
The identified vulnerability represents a critical failure in the verification process for cryptographic signatures within the Monobank payment integration module for Drupal, specifically affecting versions ranging from 0.0.0 through 1.0.3. This flaw stems directly from CWE-347, which classifies Improper Verification of Cryptographic Signature as a weakness where software does not properly verify that a received message has been signed by an authorized entity or has not been altered in transit. In the context of payment processing APIs, cryptographic signatures are essential for ensuring data integrity and authenticity. When this verification mechanism is flawed, the application fails to validate whether the incoming request originated from the legitimate Monobank server or if it has been tampered with during transmission by a third party.
The technical manifestation of this vulnerability allows an attacker to perform signature spoofing attacks against the payment API endpoint. By manipulating the payload and bypassing the signature validation logic, an adversary can forge requests that appear authentic to the Drupal application. This capability enables unauthorized actions such as altering transaction amounts, changing recipient accounts, or fabricating successful payment confirmations for transactions that never actually occurred. The root cause typically involves either a missing check for the digital signature entirely, reliance on weak hashing algorithms like MD5 without proper salting, or logic errors in how the expected signature is computed and compared against the received value. Such implementation gaps are common when developers assume security through obscurity or fail to adhere strictly to cryptographic best practices during API integration.
The operational impact of this vulnerability is severe due to its direct association with financial transactions. Successful exploitation can lead to significant financial fraud, where attackers drain merchant accounts by spoofing refunds or altering payment statuses. Beyond immediate monetary loss, the integrity of the entire e-commerce platform is compromised. Customers may receive goods without paying if an attacker spoofs a success response for a failed transaction. Furthermore, this breach undermines trust in the payment infrastructure and can result in regulatory penalties under standards such as PCI DSS, which mandates strict controls over cryptographic key management and data integrity verification during transmission. The availability of affected versions from 0.0.0 indicates that early adopters or legacy systems are particularly at risk, having never received a patch for this fundamental security oversight.
Mitigation strategies must prioritize immediate remediation through software updates. Administrators should upgrade the Monobank payment API module to version 1.0.4 or any subsequent release where the cryptographic signature verification has been corrected according to industry standards. If upgrading is not immediately feasible, temporary mitigations include implementing strict input validation and ensuring that all external API calls are routed through a secure gateway that performs secondary signature verification before passing requests to the application logic. Additionally, enabling comprehensive logging for payment-related events can aid in detecting anomalous patterns indicative of spoofing attempts. Long-term security posture improvements should involve adopting OWASP API Security Top 10 guidelines, specifically focusing on Broken Object Level Authorization and Improper Inventory Management, while ensuring that all cryptographic implementations follow NIST recommendations for key management and algorithm selection to prevent future signature forgery attacks aligned with ATT&CK techniques related to resource hijacking or financial theft.