user can still bruteforce HTTP authentication when his IP address is banned

Hello,

I would like to block a user IP address after several failed login attempts
on an Apache web server using HTTP authentication (Basic or Digest).
The configuration I am using should block an IP address after 3 errors
(HTTP 401 Unauthorized response) but I can still try as many passwords as I
want. If I try the correct password, I can see the HTTP 403 Forbidden error
page. And if I press Ctrl+Shift+Del in Firefox to clear "Active Logins", I
can continue the bruteforce again.
It looks like ModSecurity is only blocking the page behind the login but
not an actual bruteforce. Is it a ModSecurity bug or a problem with my
configuration?

I have added the following configuration in
/etc/modsecurity/modsecurity_custom_rules.conf, based on the "IP-Based
Blocking" example of
https://snippets.aktagon.com/snippets/563-brute-force-authentication-protection-with-modsecurity
(replace /testpage with a path using HTTP authentication):

<LocationMatch /testpage>
        # Uncomment to troubleshoot
        #SecDebugLogLevel 9
        #SecDebugLog /tmp/troubleshooting.log

        # Enforce an existing IP address block
        SecRule IP:bf_block "@eq 1" \
                "id:1,phase:2,deny,\
                msg:'IP address blocked because of suspected brute-force
attack'"

        # Check that this is a GET
        SecRule REQUEST_METHOD "@streq GET"
"id:2,phase:5,chain,t:none,nolog,pass"
                # AND Check for authentication failure and increment
counters
                SecRule RESPONSE_STATUS "^401" \
                        "setvar:IP.bf_counter=+1"

        # Check for too many failures from a single IP address. Block for
10 minutes.
        SecRule IP:bf_counter "@ge 3" \
                "id:3,phase:5,pass,t:none, \
                setvar:IP.bf_block,\
                setvar:!IP.bf_counter,\
                expirevar:IP.bf_block=600"
</LocationMatch>

Thanks.

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