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xss: Native cross-site scripting support in NGINX

Installation

You can install this module in any RHEL-based distribution, including, but not limited to:

  • RedHat Enterprise Linux 6, 7, 8, 9
  • CentOS 6, 7, 8, 9
  • AlmaLinux 8, 9
  • Rocky Linux 8, 9
  • Amazon Linux 2
yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install nginx-module-xss

Enable the module by adding the following at the top of /etc/nginx/nginx.conf:

load_module modules/ngx_http_xss_filter_module.so;

This document describes nginx-module-xss v0.6 released on Dec 26 2022.

xss-nginx-module - Native cross-site scripting support in nginx

Synopsis

## accessing /foo?callback=process gives the response
## body "process(...);" (without quotes) where "..."
## is the original response body of the /foo location.
server {
    location /foo {
        # your content handler goes here...

        xss_get on;
        xss_callback_arg 'callback';
        xss_input_types 'application/json'; # default
        xss_output_type 'application/x-javascript'; # default
    }
    ...
}

Description

This module adds cross-site AJAX support to nginx. Currently only cross-site GET is supported. But cross-site POST will be added in the future.

The cross-site GET is currently implemented as JSONP (or "JSON with padding"). See http://en.wikipedia.org/wiki/JSON#JSONP for more details.

Directives

xss_get

syntax: xss_get on | off

default: xss_get off

context: http, server, location, if location

Enables JSONP support for GET requests.

xss_callback_arg

syntax: xss_callback_arg <name>

default: none

context: http, http, location, if location

Specifies the JavaScript callback function name used in the responses.

For example,

location /foo {
    xss_get on;
    xss_callback_arg c;
    ...
}

then

GET /foo?c=blah

returns

blah(...);

xss_override_status

syntax: xss_override_status on | off

default: xss_check_status on

context: http, server, location, if location

Specifies whether to override 30x, 40x and 50x status to 200 when the response is actually being processed.

xss_check_status

syntax: xss_check_status on | off

default: xss_check_status on

context: http, server, location, if location

By default, ngx_xss only process responses with the status code 200 or 201.

xss_input_types

syntax: xss_input_types [mime-type]...

default: xss_input_types application/json

context: http, server, location, if location

Only processes the responses of the specified MIME types.

Example:

xss_input_types application/json text/plain;

Limitations

  • ngx_xss will not work with ngx_echo's subrequest interfaces, due to the underlying limitations imposed by subrequests' "postponed chain" mechanism in the nginx core. The standard ngx_addition module also falls into this category. You're recommended, however, to use ngx_lua as the content handler to issue subrequests and ngx_xss to do JSONP, because ngx_lua's ngx.location.capture() interface does not utilize the "postponed chain" mechanism, thus getting out of this limitation. We're taking this approach in production and it works great.

Trouble Shooting

Use the "info" error log level (or lower) to get more diagnostics when things go wrong.

TODO

  • add cross-site POST support.

Author

Yichun "agentzh" Zhang (章亦春) <agentzh@gmail@com>

The implementation of the builtin connection pool has borrowed a lot of code from Maxim Dounin's upstream_keepalive module. This part of code is copyrighted by Maxim Dounin.

This module is licenced under the BSD license.

Copyright (C) 2009-2018 by Yichun "agentzh" Zhang (章亦春) <agentzh@gmail.com> OpenResty Inc.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

See Also

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-xss.

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