CVE-2025-42601 Overview
CVE-2025-42601 is a Captcha bypass vulnerability in Meon KYC solutions. The flaw stems from insufficient server-side validation of the Captcha parameter in certain API endpoints. A remote attacker can intercept a legitimate request, strip the Captcha parameter, and submit the request without solving the challenge. The server accepts the modified request and processes it as valid. This defeats anti-automation controls that protect Know Your Customer (KYC) workflows from scripted abuse, credential stuffing, and enumeration. The vulnerability is tracked under CWE-602: Client-Side Enforcement of Server-Side Security and was disclosed in CERT-IN Advisory CIVN-2025-0082.
Critical Impact
Remote unauthenticated attackers can bypass Captcha verification on Meon KYC API endpoints, enabling automated abuse of identity verification workflows.
Affected Products
- Meon KYC solutions (specific versions not enumerated in the advisory)
- API endpoints relying on client-supplied Captcha parameters
- Identity verification workflows exposed through affected endpoints
Discovery Timeline
- 2025-04-23 - CVE-2025-42601 published to NVD
- 2026-04-15 - Last updated in NVD database
Technical Details for CVE-2025-42601
Vulnerability Analysis
The vulnerability is a business logic flaw classified under [CWE-602]. The Meon KYC backend treats the Captcha parameter as optional during request processing. When the parameter is present, the server validates it. When the parameter is absent, the server skips validation entirely and processes the request. Captcha controls are intended to enforce that a human, not a script, submits the request. Skipping validation when the parameter is missing converts the control into an opt-in check controlled by the client. This allows machine-driven submissions against endpoints designed for human-rate interaction.
Root Cause
The root cause is improper conditional validation logic on the server. Server-side code paths fail to require the Captcha token as a mandatory field. The validation routine returns success when no token is supplied instead of rejecting the request. Anti-automation security is therefore enforced client-side rather than server-side, which is the defining condition of [CWE-602].
Attack Vector
An attacker uses an intercepting proxy such as Burp Suite or mitmproxy to capture a legitimate API request to the affected KYC endpoint. The attacker removes the Captcha field, the associated token, or related verification parameters from the JSON or form body. The modified request is replayed to the server. The server processes it without enforcing the challenge. Attackers can then script repeated submissions to enumerate identity data, brute-force verification flows, or flood KYC pipelines. The attack requires network access to the API and no authentication.
No public proof-of-concept code is available. Technical details of the request modification are described in the CERT-IN advisory.
Detection Methods for CVE-2025-42601
Indicators of Compromise
- API requests to KYC endpoints missing the Captcha field or token parameter
- High-volume submissions to identity verification endpoints from a single source IP or narrow IP range
- Requests with non-browser User-Agent strings hitting endpoints normally accessed from web forms
- Successful API responses for requests that lack expected anti-automation headers or parameters
Detection Strategies
- Inspect web server and API gateway logs for KYC endpoint requests where the Captcha payload field is absent or empty
- Correlate request rate per source IP against historical baselines for KYC submission endpoints
- Deploy WAF rules that require the presence and non-empty value of the Captcha parameter before forwarding to the application
Monitoring Recommendations
- Alert on spikes in KYC endpoint traffic outside business hours or from unexpected geographies
- Forward API gateway and WAF logs to a centralized analytics platform for behavioral analysis
- Track failed and successful KYC verification ratios for anomalies indicating scripted enumeration
How to Mitigate CVE-2025-42601
Immediate Actions Required
- Contact Meon for an official patch or updated build addressing the Captcha validation logic
- Deploy a WAF rule that rejects requests to affected API endpoints when the Captcha parameter is missing or empty
- Implement rate limiting on KYC endpoints per source IP and per session
- Review API gateway logs for prior abuse and identify suspicious submissions submitted without Captcha tokens
Patch Information
The CERT-IN Advisory CIVN-2025-0082 provides vendor coordination details. Organizations using Meon KYC solutions should contact the vendor for fixed versions and apply server-side validation that treats the Captcha parameter as mandatory.
Workarounds
- Enforce mandatory Captcha parameter validation at the reverse proxy or API gateway layer until a vendor patch is applied
- Add server-side schema validation that rejects requests with missing required anti-automation fields
- Restrict access to affected KYC API endpoints by source IP allowlists where feasible
- Introduce additional bot-mitigation controls such as device fingerprinting or behavioral analysis for KYC workflows
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
