How to block Slack Image Proxy
Operated by Slack. This robot is used to fetch and cache images posted into Slack channels.
robots.txt
What the agent asks to be told. It obeys this or it does not — nothing enforces it.
User-agent: Slack-ImgProxy Disallow: /
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 ~* "(Slack-ImgProxy|Slack Image Proxy)") {
return 403;
}
Apache
In .htaccess or the vhost.
BrowserMatchNoCase "Slack-ImgProxy" bad_bot
BrowserMatchNoCase "Slack Image Proxy" 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 "Slack-ImgProxy") or (http.user_agent contains "Slack Image Proxy")
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 (['Slack-ImgProxy', 'Slack Image Proxy'] as $needle) {
if (stripos($agent, $needle) !== false) {
status_header(403);
exit('Blocked: Slack Image Proxy');
}
}
});
robots.txt is a request. The rules below it are the wall.
Slack Image Proxy publishes a token, so the directive above will work for as long as it keeps honouring it — and nothing except its own good manners makes it. 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.