How to block Cloudflare CustomerSLO Prober
Operated by Cloudflare. A service to verify the identity of Cloudflare-internal Customer SLO probes
nginx
In the server block, then reload.
nginx
# 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 ~* "(CustomerSLO Prober)") {
return 403;
}
Apache
In .htaccess or the vhost.
Apache
BrowserMatchNoCase "CustomerSLO Prober" bad_bot
<RequireAll>
Require all granted
Require not env bad_bot
</RequireAll>
Cloudflare
Security → WAF → Custom rules.
Cloudflare
# Security → WAF → Custom rules, action: Block (http.user_agent contains "CustomerSLO Prober")
WordPress
A child theme's functions.php, or a small plugin.
WordPress
// 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 (['CustomerSLO Prober'] as $needle) {
if (stripos($agent, $needle) !== false) {
status_header(403);
exit('Blocked: Cloudflare CustomerSLO Prober');
}
}
});
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.