[os-nginx] NAXSI blocked requests return HTTP 200 instead of 403

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Describe the bug
When NAXSI in the os-nginx plugin blocks a request, the request is correctly blocked internally, but the client receives HTTP 200 OK instead of an appropriate error status such as 403 Forbidden.

The generated nginx configuration uses:

DeniedUrl "/waf_denied.html";

with:

location = /waf_denied.html {
    root /usr/local/etc/nginx/views;
    access_log /var/log/nginx/waf_denied.access.log main;
}

Because this location serves the static denial page without explicitly returning an error status, the resulting response is HTTP 200.

I do not know a last known working version. The behavior is reproducible on my current installation.

To Reproduce
Steps to reproduce the behavior:

1. Go to Services > Nginx > Configuration > HTTP(S) > Naxsi WAF Rule.

2. Create a Basic Rule matching a test URL, for example:

   ^/xmlrpc\.php/?$
   

   with score 8.

3. Add the rule to a Custom Security Policy configured as:

   Value: 8
   Operator: >=
   Action: BLOCK
   

4. Enable Security Rules on the applicable nginx Location and assign the Custom Security Policy.

5. Apply the nginx configuration.

6. Request the blocked URL:

   curl -sS -o /dev/null -w '%{http_code}\n' https://example.com/xmlrpc.php
   

7. The returned HTTP status is:

   200
   

8. The nginx error log simultaneously confirms that NAXSI blocked the original request:

   NAXSI_FMT: ... uri=/xmlrpc.php&config=block&...&score0=8&zone0=URL&id0=...
   

9. The request is also written to:

   /var/log/nginx/waf_denied.access.log
   

   where the denial response is logged with status 200.

The blocked request does not reach the upstream application, so the WAF itself is functioning correctly.

Expected behavior
A request blocked by NAXSI should return an HTTP error status, preferably:

403 Forbidden

instead of:

200 OK

The denial page may still be displayed, but it should be returned with the correct HTTP status.

Screenshots
Not required for reproduction. I can provide screenshots of the NAXSI rule, policy and Location configuration if needed.

Relevant log files
Example nginx error log entry:

NAXSI_FMT: ... server=example.com&uri=/xmlrpc.php&config=block&...&score0=8&zone0=URL&id0=...

At the same time, /var/log/nginx/waf_denied.access.log records the blocked request with HTTP status 200.

For example:

"GET /xmlrpc.php HTTP/2.0" 200 ...

The generated configuration contains:

DeniedUrl "/waf_denied.html";

location = /waf_denied.html {
    root /usr/local/etc/nginx/views;
    access_log /var/log/nginx/waf_denied.access.log main;
}

Additional context
This does not appear to be a WAF bypass. NAXSI correctly detects and blocks the request before it reaches the upstream application.

The problem is the final HTTP status returned to the client. Reporting a blocked request as 200 OK can produce misleading results in vulnerability scanners, monitoring systems, access logs and other automated security tooling.

A possible solution would be for the generated NAXSI denial handler to preserve or explicitly return a 403 status, for example by making the denial location internal and returning HTTP 403 while still optionally serving the existing denial page.

Environment
OPNsense: OPNsense 26.7.2_2-amd64
FreeBSD 15.1-RELEASE-p2
OpenSSL 3.5.7
os-nginx plugin: os-nginx (installed) | 1.36_4
Hardware: DEC850v2

Start at Services > Nginx > Configuration > HTTP(S) > Naxsi WAF Rule and inspect how the generated DeniedUrl location is produced. Reproduce with the supplied curl command and compare the nginx error and waf_denied access logs; done means blocked requests return 403 while the denial page may still be displayed and the upstream is not reached.