SCG WS nginx

NginX Secure Configuration Guide

Summary
This provides NginX security configuration harden guide. The configuration guide is focused on the NginX itself. Therefore, the Linux OS configuration hardening is not covered here.

It includes the following topic: 2.1 Buffer Overflow Protection 2.2 Remove Unnecessary backup files 2.3 Remove Version number 2.4 Mitigating Slow HTTP DoS Attack 2.5 Allow Access To Specified Domain Only 2.6 Limit IP clients access 2.7 SSL/TLS Configuration 2.8 SSL Module 2.9 HTTP secure Header 2.10 Limit HTTP Method

Buffer Overflow Protection
client_body_buffer_size 100K; client_header_buffer_size 1k; client_max_body_size 100k; large_client_header_buffers 2 1k;
 * 1) Size Limits & Buffer Overflows
 * 2) the size may be configured based on the needs.

Refer here for detailed of each configuration value. http://nginx.org/en/docs/http/ngx_http_core_module.html

Based on CIS Appache configuration guide
 * Limit the size of Http request header to 1024 bytes or less
 * Limits the number of bytes that are allowed in a request body to 102400 or les

Remove Unnecessary backup files
Use the following command to search if there is any unnecessary backup files to be removed.
 * 1) find /nginx -name '.?*' -not -name .ht* -or -name '*~' -or -name '*.bak*' -or -name '*.old*'
 * 2) find /usr/local/nginx/html/ -name '.?*' -not -name .ht* -or -name '*~' -or -name '*.bak*' -or -name '*.old*'

Remove Version number
server_tokens off;
 * 1) Display nginx Version number in error or http header may result in hacker to search for known vulnerability.
 * 2) Therefore, the version number should be removed for every http response.

Mitigating Slow HTTP DoS Attack
client_body_timeout  10; client_header_timeout 10; keepalive_timeout    5 5; send_timeout         10;
 * 1) Timeouts definition ##
 * 1) End ##
 * client_body_timeout: Defines a timeout for reading client request body. The timeout is set only for a period between two successive read operations, not for the transmission of the whole request body. If a client does not transmit anything within this time, the 408 (Request Time-out) error is returned to the client.
 * client_header_timeout: Defines a timeout for reading client request header. If a client does not transmit the entire header within this time, the 408 (Request Time-out) error is returned to the client.
 * keepalive_timeout: The first parameter sets a timeout during which a keep-alive client connection will stay open on the server side. The zero value disables keep-alive client connections. The optional second parameter sets a value in the “Keep-Alive: timeout=time” response header field. Two parameters may differ. The “Keep-Alive: timeout=time” header field is recognized by Mozilla and Konqueror. MSIE closes keep-alive connections by itself in about 60 seconds.
 * send_timeout: Sets a timeout for transmitting a response to the client. The timeout is set only between two successive write operations, not for the transmission of the whole response. If the client does not receive anything within this time, the connection is closed.

Refer here for detailed of each configuration value. http://nginx.org/en/docs/http/ngx_http_core_module.html

Allow Access To Specified Domain Only
if ($host !~ ^(abc.com|www.abc.com|images.abc.com)$ ) { return 444; }
 * 1)  i.e. abc.com, images.abc.com and www.abc.com

Limit IP clients access
Limit specific folder to certain source IP clients only.

## the docs folder is only allowed specific IP range in 192.168.1.0/24

location /docs/ { ## block one workstation deny   192.168.1.1; ## allow anyone in 192.168.1.0/24 allow  192.168.1.0/24; ## drop rest of the world deny   all; }

SSL/TLS Configuration
Disable SSLv3(enabled by default since nginx 0.8.19) server { # SSL protocols TLS v1~TLSv1.2 are allowed. Disabed SSLv3 ssl_protocols TLSv1 TLSv1.1 TLSv1.2; }

For further details on SSL Module configuration refer to http://wiki.nginx.org/NginxHttpSslModule

SSL Module
server { # enables server-side protection from BEAST attacks ssl_prefer_server_ciphers on;

# Disabled insecure ciphers suite. For example, MD5, DES, RC4, PSK ssl_ciphers "ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA256:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES256-GCM-SHA384:AES128-GCM-SHA256:AES256-SHA256:AES128-SHA256:AES256-SHA:AES128-SHA:DES-CBC3-SHA:HIGH:!aNULL:!eNULL:!EXPORT:!DES:!MD5:!PSK:!RC4:@STRENGTH";

# -!MEDIUM：exclude encryption cipher suites using 128 bit encryption. # -!LOW：  exclude encryption cipher suites using 64 or 56 bit encryption algorithms # -!EXPORT： exclude export encryption algorithms including 40 and 56 bits algorithms. # -!aNULL： exclude the cipher suites offering no authentication. This is currently the anonymous DH algorithms and anonymous ECDH algorithms. These cipher suites are vulnerable to a "man in the middle" attack and so their use is normally discouraged. # -!eNULL：exclude the "NULL" ciphers that is those offering no encryption. Because these offer no encryption at all and are a security risk they are disabled unless explicitly included. # @STRENGTH：sort the current cipher list in order of encryption algorithm key length.

}

HTTP secure Header
add_header X-Frame-Options SAMEORIGIN;
 * 1) X-Frame-Options is to prevent from clickJacking attack

add_header X-Content-Type-Options nosniff;
 * 1)  disable content-type sniffing on some browsers.

add_header X-XSS-Protection "1; mode=block";
 * 1) This header enables the Cross-site scripting (XSS) filter

add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";
 * 1) This will enforce HTTP browsing into HTTPS and avoid ssl stripping attack

refer to https://www.owasp.org/index.php/List_of_useful_HTTP_headers

Limit HTTP Method
if ($request_method !~ ^(GET|PUT|POST)$ ) { return 444; }
 * 1) Only GET, Post, PUT are allowed##
 * 1) In this case, it does not accept other HTTP method such as HEAD, DELETE, SEARCH, TRACE ##

In most of cases, the TRACE method is suggested to be disabled.