How to block Netcraft SSL Server Survey
Operated by Netcraft. Netcraft SSL Server Survey is a security scanner operated by Netcraft, a cybersecurity and digital risk protection company. This bot scans websites to collect SSL/TLS certificate information as part of their threat intelligence operations and web infrastructure security analysis.
How it identifies itself
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; Netcraft SSL Server Survey - contact [email protected])
nginx
In the server block, then reload.
# In the server block. 403 rather than 444: a closed connection tells the
# operator nothing, and an agent that gets a status code can log it.
if ($http_user_agent ~* "(Netcraft SSL Server Survey)") {
return 403;
}
Apache
In .htaccess or the vhost.
BrowserMatchNoCase "Netcraft SSL Server Survey" bad_bot
<RequireAll>
Require all granted
Require not env bad_bot
</RequireAll>
Cloudflare
Security → WAF → Custom rules.
# Security → WAF → Custom rules, action: Block (http.user_agent contains "Netcraft SSL Server Survey")
WordPress
A child theme's functions.php, or a small plugin.
// functions.php of a child theme, or a small plugin. Runs before WordPress
// builds the page, so a blocked agent costs one PHP process and no queries.
add_action('init', function () {
$agent = $_SERVER['HTTP_USER_AGENT'] ?? '';
foreach (['Netcraft SSL Server Survey'] as $needle) {
if (stripos($agent, $needle) !== false) {
status_header(403);
exit('Blocked: Netcraft SSL Server Survey');
}
}
});
A rule on the user agent is a rule on a string it chose
The server rules match on a header the requester sets, which stops the agent that says who it is and not the one that copies somebody else's name. Botscope verifies identity against DNS and published address ranges, records which check decided each request, and shows you the ones that lied.