Contact Form 7 Validation Issues – A potential solution

We’re running CF7 v5.5.4 on a WordPress 5.8.1 multi-site install. We experienced a problem similar to that of many recent users that our CF7 reCAPTCHA integration (both V3 and v2 (w/ plugin)) was not successfully validating. We followed the initial troubleshooting steps (removing all plugins except for CF7 and using a default theme), but this unfortunately didn’t solve our issue.

Following extensive troubleshooting and testing on a variety of different WP platforms, we discovered that our issue was caused by an idiosyncrasy of the cURL resolver, which prioritizes connections by IPv6 over those of IPv4 (https://askubuntu.com/questions/32298/prefer-a-ipv4-dns-lookups-before-aaaaipv6-lookups).

As CF7 (similar to many other plugins) does not specify IPv4/6 when attempting to connect to Google (https://www.google.com/recaptcha/api/siteverify), cURL libraries that include IPv6 simultaneously run DNS lookups for both IPv4 and IPv6. On production servers such as ours that don’t use IPv6, cURL waits for a timeout error on IPv6 before attempting the IPv4 connection. This short delay is enough to break the reCAPTCHA verification, and is very difficult to spot without careful tracing of network traffic. Note, this isn’t a bug in CF7 per se, but it will break CF7’s reCAPTCHA integration for certain users.

Our IT administrator was able to solve the problem by installing a small plugin (https://gist.github.com/golderweb/3a2aaec2d56125cc004e) that deactivates IPv6 on cURL. After the installation of this plugin (which can be done on individual sites on a multisite WP install), CF7 DNS lookups are restricted to IPv4, resulting in a quick response and a successful reCAPTCHA validation. Note – this is only an issue if your cURL library has been compiled to use IPv6, which is likely the reason why folks’ recent success with CF7 has been mixed. We struggled with this issue for days before finding a solution, and I wanted to pass this on in the hopes that it will save other users some time and frustration. Note – this may not solve everyone’s issues, its definitely worth a shot after you’ve tried the general troubleshooting steps recommended by Takayuki.

• This topic was modified 2 years, 9 months ago by bueebrooklyn.