CVE-2025-42601 is a vulnerability identified in Meon KYC (Know Your Customer) solutions version 1.1, stemming from improper security design where client-side enforcement is relied upon for server-side security controls. Specifically, the vulnerability arises due to insufficient server-side validation of the Captcha parameter in certain API endpoints. Captchas are typically used to prevent automated abuse by verifying that a user is human. In this case, the Meon KYC solution's API endpoints accept requests with a Captcha parameter, but the server does not adequately verify its presence or validity. Consequently, a remote attacker can intercept legitimate API requests and remove or alter the Captcha parameter before forwarding the request to the server. Because the server does not enforce Captcha validation, the attacker effectively bypasses the Captcha mechanism, potentially automating interactions with the KYC system without restriction. This flaw is categorized under CWE-602, which involves client-side enforcement of security controls that should be enforced on the server side. The vulnerability does not require authentication or user interaction beyond intercepting and modifying requests, making exploitation feasible for attackers with network access to the API endpoints. Although no known exploits are currently reported in the wild, the vulnerability poses a risk of automated abuse, such as mass fraudulent KYC submissions, denial of service through automated requests, or other manipulations that could undermine the integrity of the KYC process. Given that KYC solutions are critical for identity verification in financial and regulated sectors, this vulnerability could be leveraged to facilitate fraud, money laundering, or unauthorized access to services relying on Meon KYC for identity validation.

For European organizations, particularly those in the financial services, banking, and regulatory compliance sectors, this vulnerability could have significant consequences. The bypass of Captcha verification enables attackers to automate fraudulent KYC submissions, potentially allowing illicit actors to create fake or synthetic identities. This undermines anti-money laundering (AML) and counter-terrorism financing (CTF) efforts, increasing regulatory and legal risks for organizations. Additionally, automated abuse could degrade service availability by overwhelming API endpoints, impacting legitimate users and causing operational disruptions. The integrity of customer identity data could be compromised, leading to reputational damage and potential financial losses. Organizations relying on Meon KYC solutions for onboarding or identity verification may face increased exposure to fraud and compliance violations. Given the stringent data protection and financial regulations in Europe, such as GDPR and the EU’s AML directives, failure to adequately secure KYC processes could result in regulatory penalties and loss of customer trust.

To mitigate this vulnerability, organizations using Meon KYC solutions should implement the following specific measures: 1) Apply server-side validation for all security controls, especially Captcha verification, ensuring that the server rejects any requests missing valid Captchas regardless of client-side input. 2) Employ API gateways or web application firewalls (WAFs) to detect and block requests that lack expected Captcha parameters or exhibit automated behavior patterns. 3) Implement rate limiting and anomaly detection on KYC API endpoints to identify and throttle suspicious traffic indicative of automated abuse. 4) Use strong encryption and secure transport (e.g., TLS) to prevent interception and tampering of API requests in transit. 5) Engage with Meon to obtain patches or updates addressing this vulnerability once available, and prioritize their deployment. 6) Conduct regular security assessments and penetration testing focused on API security and input validation. 7) Monitor logs for unusual patterns of KYC submissions that may indicate exploitation attempts. These measures go beyond generic advice by focusing on compensating controls and proactive detection until a vendor patch is released.