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Fix CAPTCHA Loop After Verification

Why Am I Stuck in a CAPTCHA Loop Even After Verification?​

If you have successfully completed the CAPTCHA verification but are still being prompted again, this is a known behavior related to DNS caching on your server.

Root Cause​

cPGuard uses the ModSecurity DNSBL (DNS-based Blocklist) option to validate the reputation of the client's IP address. This process relies on DNS queries, and the responses are sent with a 10-second TTL (Time To Live).

On some systems, this TTL is not respected and the DNS response is cached for longer than expected. As a result, the reputation status takes more time to reflect, causing repeated CAPTCHA verification prompts.

CAPTCHA Versions in cPGuard​

cPGuard provides two CAPTCHA versions to address this issue. Understanding the difference will help you choose the right option for your environment.

CAPTCHA V1 (Legacy) — Recommended by Default​

The legacy CAPTCHA option is the recommended default for most users. It is:

  • Lightweight and simple
  • Does not require any additional components or binary execution
  • Sufficient for the majority of server environments
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If your server uses reliable open name servers that respect DNS TTLs, V1 will work without any issues.

CAPTCHA V2 — Optional, for DNS Caching Issues​

CAPTCHA V2 is an advanced option designed specifically for servers that experience DNS caching issues with V1. It works by:

  • Bypassing DNS caching by sending the query through a binary
  • Adding an additional verification layer to the CAPTCHA system

However, V2 comes with trade-offs:

  • More resource-intensive than V1
  • Involves binary execution, making it less lightweight
  • Adds complexity compared to the simpler V1 ruleset
note

V2 is recommended only if you are experiencing a CAPTCHA loop with the legacy (V1) option. It is not intended as a replacement for V1 in standard environments.

How to Fix the CAPTCHA Loop​

Enable CAPTCHA V2​

Switch to CAPTCHA V2 to bypass the DNS caching issue.

To enable CAPTCHA V2, navigate to:

App Portal >> Settings >> WAF & Bruteforce >> Captcha protection V2

WAF CAPTCHA V2

tip

If you continue to experience issues after trying both options, please contact our support team for further assistance.