Security tuning

BunkerWeb offers many security features that you can configure with settings. Even if the default values of settings ensure a minimal "security by default", we strongly recommend you tune them. By doing so you will be able to ensure the security level of your choice but also manage false positives.

Other settings

This section only focuses on security tuning, see the settings section of the documentation for other settings.

Overview and order of the core security plugins

HTTP protocol

Deny status code

The first thing to define is the kind of action to do when a client access is denied. You can control the action with the DENY_HTTP_STATUS setting which allows the following values :

• 403 : send a "classical" Forbidden HTTP status code (a web page or custom content will be displayed)
• 444 : close the connection (no web page or custom content will be displayed)

The default value is 403 and we suggest you set it to 444 only if you already fixed a lot of false positive, you are familiar with BunkerWeb and want a higher level of security.

Default server

In the HTTP protocol, the Host header is used to determine which server the client wants to send the request to. That header is facultative and may be missing from the request or can be set as an unknown value. This is a common case, a lot of bots are scanning the Internet and are trying to exploit services or simply doing some fingerprinting.

You can disable any request containing undefined or unknown Host value by setting DISABLE_DEFAULT_SERVER to yes (default : no). Please note that clients won't even receive a response, the TCP connection will be closed (using the special 444 status code of NGINX).

Allowed methods

You can control the allowed HTTP methods by listing them (separated with "|") in the ALLOWED_METHODS setting (default : GET|POST|HEAD). Clients sending a method which is not listed will get a "405 - Method Not Allowed".

Max sizes

You can control the maximum body size with the MAX_CLIENT_SIZE setting (default : 10m). See here for accepted values. You can use the special value 0 to allow a body of infinite size (not recommended).

Serve files

To disable serving files from the www folder, you can set SERVE_FILES to no (default : yes). The value no is recommended if you use BunkerWeb as a reverse proxy.

Headers

Headers are very important when it comes to HTTP security. While some of them might be too verbose, others' verbosity will need to be increased, especially on the client-side.

Remove headers

You can automatically remove verbose headers in the HTTP responses by using the REMOVE_HEADERS setting (default : Server X-Powered-By X-AspNet-Version X-AspNetMvc-Version).

Cookies

When it comes to cookies security, we can use the following flags :

• HttpOnly : disable any access to the cookie from Javascript using document.cookie
• SameSite : policy when requests come from third-party websites
• Secure : only send cookies on HTTPS request

Cookie flags can be overridden with values of your choice by using the COOKIE_FLAGS setting (default : * HttpOnly SameSite=Lax). See here for accepted values.

The Secure flag can be automatically added if HTTPS is used by using the COOKIE_AUTO_SECURE_FLAG setting (default : yes). The value no is not recommended unless you know what you're doing.

Security headers

Various security headers are available and most of them can be set using BunkerWeb settings. Here is the list of headers, the corresponding setting and default value :

Header	Setting	Default
Content-Security-Policy	CONTENT_SECURITY_POLICY	object-src 'none'; frame-src 'self'; child-src 'self'; form-action 'self'; frame-ancestors 'self';
Strict-Transport-Security	STRICT_TRANSPORT_SECURITY	max-age=31536000
Referrer-Policy	REFERRER_POLICY	strict-origin-when-cross-origin
Permissions-Policy	PERMISSIONS_POLICY	accelerometer=(), ambient-light-sensor=(), autoplay=(), battery=(), camera=(), cross-origin-isolated=(), display-capture=(), document-domain=(), encrypted-media=(), execution-while-not-rendered=(), execution-while-out-of-viewport=(), fullscreen=(), geolocation=(), gyroscope=(), hid=(), idle-detection=(), magnetometer=(), microphone=(), midi=(), navigation-override=(), payment=(), picture-in-picture=(), publickey-credentials-get=(), screen-wake-lock=(), serial=(), usb=(), web-share=(), xr-spatial-tracking=()
Feature-Policy	FEATURE_POLICY	accelerometer 'none'; ambient-light-sensor 'none'; autoplay 'none'; battery 'none'; camera 'none'; display-capture 'none'; document-domain 'none'; encrypted-media 'none'; execution-while-not-rendered 'none'; execution-while-out-of-viewport 'none'; fullscreen 'none'; 'none'; geolocation 'none'; gyroscope 'none'; layout-animation 'none'; legacy-image-formats 'none'; magnetometer 'none'; microphone 'none'; midi 'none'; navigation-override 'none'; payment 'none'; picture-in-picture 'none'; publickey-credentials-get 'none'; speaker-selection 'none'; sync-xhr 'none'; unoptimized-images 'none'; unsized-media 'none'; usb 'none'; screen-wake-lock 'none'; web-share 'none'; xr-spatial-tracking 'none';
X-Frame-Options	X_FRAME_OPTIONS	SAMEORIGIN
X-Content-Type-Options	X_CONTENT_TYPE_OPTIONS	nosniff
X-XSS-Protection	X_XSS_PROTECTION	1; mode=block

CORS

Cross-Origin Resource Sharing lets you manage how your service can be contacted from different origins. Please note that you will have to allow the OPTIONS HTTP method using the ALLOWED_METHODS if you want to enable it (more info here). Here is the list of settings related to CORS :

Setting	Default	Context	Multiple	Description
USE_CORS	no	multisite	no	Use CORS
CORS_ALLOW_ORIGIN	*	multisite	no	Value of the Access-Control-Allow-Origin header.
CORS_EXPOSE_HEADERS	Content-Length,Content-Range	multisite	no	Value of the Access-Control-Expose-Headers header.
CORS_MAX_AGE	86400	multisite	no	Value of the Access-Control-Max-Age header.
CORS_ALLOW_CREDENTIALS	no	multisite	no	Send the Access-Control-Allow-Credentials header.
CORS_ALLOW_METHODS	GET, POST, OPTIONS	multisite	no	Value of the Access-Control-Allow-Methods header.
CORS_ALLOW_HEADERS	DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range	multisite	no	Value of the Access-Control-Allow-Headers header.

HTTPS

Besides the HTTPS configuration, the following settings related to HTTPS can be set :

Setting	Default	Description
REDIRECT_HTTP_TO_HTTPS	no	When set to yes, will redirect every HTTP request to HTTPS even if BunkerWeb is not configured with HTTPS.
AUTO_REDIRECT_HTTP_TO_HTTPS	yes	When set to yes, will redirect every HTTP request to HTTPS only if BunkerWeb is configured with HTTPS.
HTTPS_PROTOCOLS	TLSv1.2 TLSv1.3	List of supported SSL/TLS protocols when HTTPS is enabled.
HTTP2	yes	When set to yes, will enable HTTP2 protocol support when using HTTPS.
LISTEN_HTTP	yes	When set to no, BunkerWeb will not listen for HTTP requests. Useful if you want HTTPS only for example.

Let's Encrypt

BunkerWeb comes with automatic Let's Encrypt certificate generation and renewal. This is the easiest way of getting HTTPS working out of the box for public-facing web applications. Please note that you will need to set up proper DNS A record(s) for each of your domains pointing to your public IP(s) where BunkerWeb is accessible.

Here is the list of related settings :

Setting	Default	Description
AUTO_LETS_ENCRYPT	no	When set to yes, HTTPS will be enabled with automatic certificate generation and renewal from Let's Encrypt.
EMAIL_LETS_ENCRYPT	contact@{FIRST_SERVER}	Email to use when generating certificates. Let's Encrypt will send notifications to that email like certificate expiration.
USE_LETS_ENCRYPT_STAGING	no	When set to yes, the staging server of Let's Encrypt will be used instead of the production one. Useful when doing tests to avoid being "blocked" due to limits.

Custom certificate

If you want to use your own certificates, here is the list of related settings :

Setting	Default	Description
USE_CUSTOM_HTTPS	no	When set to yes, HTTPS will be enabled with custom certificates.
CUSTOM_HTTPS_CERT		Full path to the certificate. If you have one or more intermediate certificate(s) in your chain of trust, you will need to provide the bundle (more info here).
CUSTOM_HTTPS_KEY		Full path to the private key.

When USE_CUSTOM_HTTPS is set to yes, BunkerWeb will check every day if the custom certificate specified in CUSTOM_HTTPS_CERT is modified and will reload NGINX if that's the case.

Self-signed

If you want to quickly test HTTPS for staging/dev environment you can configure BunkerWeb to generate self-signed certificates, here is the list of related settings :

Setting	Default	Description
GENERATE_SELF_SIGNED_SSL	no	When set to yes, HTTPS will be enabled with automatic self-signed certificate generation and renewal from Let's Encrypt.
SELF_SIGNED_SSL_EXPIRY	365	Number of days for the certificate expiration (-days value used with openssl).
SELF_SIGNED_SSL_SUBJ	/CN=www.example.com/	Certificate subject to use (-subj value used with openssl).

ModSecurity

ModSecurity is integrated and enabled by default alongside the OWASP Core Rule Set within BunkerWeb. Here is the list of related settings :

Setting	Default	Description
USE_MODSECURITY	yes	When set to yes, ModSecurity will be enabled.
USE_MODSECURITY_CRS	yes	When set to yes and USE_MODSECURITY is also set to yes, the OWASP Core Rule Set will be loaded.

We strongly recommend keeping both ModSecurity and the OWASP Core Rule Set enabled. The only downsides are the false positives that may occur. But they can be fixed with some efforts and the CRS team maintains a list of exclusions for common applications (e.g., WordPress, Nextcloud, Drupal, Cpanel, ...).

Tuning ModSecurity and the CRS can be done using custom configurations :

• modsec-crs : before the OWASP Core Rule Set is loaded
• modsec : after the OWASP Core Rule Set is loaded (also used if CRS is not loaded)

For example, you can add a custom configuration with type modsec-crs to add CRS exclusions :

SecAction \
 "id:900130,\
  phase:1,\
  nolog,\
  pass,\
  t:none,\
  setvar:tx.crs_exclusions_wordpress=1"

You can also add a custom configuration with type modsec to update loaded CRS rules :

SecRule REQUEST_FILENAME "/wp-admin/admin-ajax.php" "id:1,ctl:ruleRemoveByTag=attack-xss,ctl:ruleRemoveByTag=attack-rce"
SecRule REQUEST_FILENAME "/wp-admin/options.php" "id:2,ctl:ruleRemoveByTag=attack-xss"
SecRule REQUEST_FILENAME "^/wp-json/yoast" "id:3,ctl:ruleRemoveById=930120"

Bad behavior

When attackers search for and/or exploit vulnerabilities they might generate some "suspicious" HTTP status codes that a "regular" user won’t generate within a period of time. If we detect that kind of behavior we can ban the offending IP address and force the attacker to come up with a new one.

That kind of security measure is implemented and enabled by default in BunkerWeb and is called "Bad behavior". Here is the list of the related settings :

Setting	Default	Description
USE_BAD_BEHAVIOR	yes	When set to yes, the Bad behavior feature will be enabled.
BAD_BEHAVIOR_STATUS_CODES	400 401 403 404 405 429 444	List of HTTP status codes considered as "suspicious".
BAD_BEHAVIOR_BAN_TIME	86400	The duration time (in seconds) of a ban when a client reached the threshold.
BAD_BEHAVIOR_THRESHOLD	10	Maximum number of "suspicious" HTTP status codes within the time period.
BAD_BEHAVIOR_COUNT_TIME	60	Period of time during which we count "suspicious" HTTP status codes.

In other words, with the default values, if a client generates more than 10 status codes from the list 400 401 403 404 405 429 444 within 60 seconds their IP address will be banned for 86400 seconds.

Antibot

Attackers will certainly use automated tools to exploit/find some vulnerabilities in your web applications. One countermeasure is to challenge the users to detect if they look like a bot. If the challenge is solved, we consider the client as "legitimate" and they can access the web application.

That kind of security is implemented but not enabled by default in BunkerWeb and is called "Antibot". Here is the list of supported challenges :

• Cookie : send a cookie to the client, we expect to get the cookie back on other requests
• Javascript : force a client to solve a computation challenge using Javascript
• Captcha : force the client to solve a classical captcha (no external dependencies)
• hCaptcha : force the client to solve a captcha from hCaptcha
• reCAPTCHA : force the client to get a minimum score with Google reCAPTCHA

Here is the list of related settings :

Setting	Default	Description
USE_ANTIBOT	no	Accepted values to enable Antibot feature : cookie, javascript, captcha, hcaptcha and recaptcha.
ANTIBOT_URI	/challenge	URI that clients will be redirected to in order to solve the challenge. Be sure that it isn't used in your web application.
ANTIBOT_SESSION_SECRET	random	The secret used to encrypt cookies when using Antibot. The special value random will generate one for you. Be sure to set it when you use a clustered integration (32 chars).
ANTIBOT_HCAPTCHA_SITEKEY and ANTIBOT_RECAPTCHA_SITEKEY		The Sitekey value to use when USE_ANTIBOT is set to hcaptcha or recaptcha.
ANTIBOT_HCAPTCHA_SECRET and ANTIBOT_RECAPTCHA_SECRET		The Secret value to use when USE_ANTIBOT is set to hcaptcha or recaptcha.
ANTIBOT_RECAPTCHA_SCORE	0.7	The minimum score that clients must have when USE_ANTIBOT is set to recaptcha.

Blacklisting, whitelisting and greylisting

The blacklisting security feature is very easy to understand : if a specific criteria is met, the client will be banned. As for the whitelisting, it's the exact opposite : if a specific criteria is met, the client will be allowed and no additional security check will be done. Whereas for the greylisting : if a specific criteria is met, the client will be allowed but additional security checks will be done.

You can configure blacklisting, whitelisting and greylisting at the same time. If that's the case, note that whitelisting is executed before blacklisting and greylisting : even if a criteria is true for all of them, the client will be whitelisted.

Blacklisting

You can use the following settings to set up blacklisting :

Setting	Default	Description
USE_BLACKLIST	yes	When set to yes, will enable blacklisting based on various criteria.
BLACKLIST_IP		List of IPs and networks to blacklist.
BLACKLIST_IP_URLS	https://www.dan.me.uk/torlist/?exit	List of URL containing IP and network to blacklist. The default list contains TOR exit nodes.
BLACKLIST_RDNS	.shodan.io .censys.io	List of reverse DNS to blacklist.
BLACKLIST_RDNS_URLS		List of URLs containing reverse DNS to blacklist.
BLACKLIST_ASN		List of ASN to blacklist.
BLACKLIST_ASN_URLS		List of URLs containing ASN to blacklist.
BLACKLIST_USER_AGENT		List of User-Agents to blacklist.
BLACKLIST_USER_AGENT_URLS	https://raw.githubusercontent.com/mitchellkrogza/nginx-ultimate-bad-bot-blocker/master/_generator_lists/bad-user-agents.list	List of URLs containing User-Agent(s) to blacklist.
BLACKLIST_URI		List of requests URI to blacklist.
BLACKLIST_URI_URLS		List of URLs containing request URI to blacklist.

Greylisting

You can use the following settings to set up greylisting :

Setting	Default	Description
USE_GREYLIST	no	When set to yes, will enable greylisting based on various criteria.
GREYLIST_IP		List of IPs and networks to greylist.
GREYLIST_IP_URLS		List of URL containing IP and network to greylist.
GREYLIST_RDNS		List of reverse DNS to greylist.
GREYLIST_RDNS_URLS		List of URLs containing reverse DNS to greylist.
GREYLIST_ASN		List of ASN to greylist.
GREYLIST_ASN_URLS		List of URLs containing ASN to greylist.
GREYLIST_USER_AGENT		List of User-Agents to greylist.
GREYLIST_USER_AGENT_URLS		List of URLs containing User-Agent(s) to greylist.
GREYLIST_URI		List of requests URI to greylist.
GREYLIST_URI_URLS		List of URLs containing request URI to greylist.

Whitelisting

You can use the following settings to set up whitelisting :

Setting	Default	Description
USE_WHITELIST	yes	When set to yes, will enable whitelisting based on various criteria.
WHITELIST_IP	20.191.45.212 40.88.21.235 40.76.173.151 40.76.163.7 20.185.79.47 52.142.26.175 20.185.79.15 52.142.24.149 40.76.162.208 40.76.163.23 40.76.162.191 40.76.162.247 54.208.102.37 107.21.1.8	List of IP and network to whitelist. The default list contains IP from DuckDuckGo crawler.
WHITELIST_IP_URLS	``	List of URLs containing IP and network to whitelist.
WHITELIST_RDNS	.google.com .googlebot.com .yandex.ru .yandex.net .yandex.com .search.msn.com .baidu.com .baidu.jp .crawl.yahoo.net .fwd.linkedin.com .twitter.com .twttr.com .discord.com	List of reverse DNS to whitelist. Default list contains various reverse DNS of search engines and social media crawlers.
WHITELIST_RDNS_URLS		List of URLs containing reverse DNS to whitelist.
WHITELIST_ASN	32934	List of ASN to whitelist. The default list contains the ASN of Facebook.
WHITELIST_ASN_URLS		List of URL containing ASN to whitelist.
WHITELIST_USER_AGENT		List of User-Agent to whitelist.
WHITELIST_USER_AGENT_URLS		List of URLs containing User-Agent to whitelist.
WHITELIST_URI		List of requests URI to whitelist.
WHITELIST_URI_URLS		List of URLs containing request(s) URI to whitelist.

BunkerNet

BunkerNet is a crowdsourced database of malicious requests shared between all BunkerWeb instances over the world.

If you enable BunkerNet, malicious requests will be sent to a remote server and will be analyzed by our systems. By doing so, we can extract malicious data from everyone's reports and give back the results to each BunkerWeb instances participating into BunkerNet.

At the moment, that feature should be considered in "beta". We only extract malicious IP and we are very strict about how we do it to avoid any "poisoning". We strongly recommend activating it (which is the default) because the more instances participate, the more data we have to improve the algorithm.

The setting used to enable or disable BunkerNet is USE_BUNKERNET (default : yes).

DNSBL

DNSBL or "DNS BlackList" is an external list of malicious IPs that you query using the DNS protocol. Automatic querying of that kind of blacklist is supported by BunkerWeb. If a remote DNSBL server of your choice says that the IP address of the client is in the blacklist, it will be banned.

Here is the list of settings related to DNSBL :

Setting	Default	Description
USE_DNSBL	yes	When set to yes, will enable DNSBL checking.
DNSBL_LIST	bl.blocklist.de problems.dnsbl.sorbs.net sbl.spamhaus.org xbl.spamhaus.org	List of DNSBL servers to ask.

Limiting

BunkerWeb supports applying a limit policy to :

• Number of connections per IP
• Number of requests per IP and URL within a time period

Please note that it should not be considered as an effective solution against DoS or DDoS but rather as an anti-bruteforce measure or rate limit policy for API.

In both cases (connections or requests) if the limit is reached, the client will receive the HTTP status "429 - Too Many Requests".

Connections

The following settings are related to the Limiting connections feature :

Setting	Default	Description
USE_LIMIT_CONN	yes	When set to yes, will limit the maximum number of concurrent connections for a given IP.
LIMIT_CONN_MAX_HTTP1	10	Maximum number of concurrent connections when using HTTP1 protocol.
LIMIT_CONN_MAX_HTTP2	100	Maximum number of concurrent streams when using HTTP2 protocol.

Requests

The following settings are related to the Limiting requests feature :

Setting	Default	Description
USE_LIMIT_REQ	yes	When set to yes, will limit the number of requests for a given IP on each URL within a period of time.
LIMIT_REQ_URL	/	The URL that will be limited. The special URL / will define a default limit for all URLs.
LIMIT_REQ_RATE	2r/s	The limit to apply to the corresponding URL. Syntax is Xr/Y where X is the number of request(s) and Y the period of time (s for second, m for minute, h for hour and d for day).

Please note that you can add different rates for different URLs by adding a number as a suffix to the settings for example : LIMIT_REQ_URL_1=/url1, LIMIT_REQ_RATE_1=5r/d, LIMIT_REQ_URL_2=/url2, LIMIT_REQ_RATE_2=1r/m, ...

Another important thing to note is that LIMIT_REQ_URL accepts LUA patterns.

Country

The country security feature allows you to apply policy based on the country of the IP address of clients :

• Deny any access if the country is in a blacklist
• Only allow access if the country is in a whitelist (other security checks will still be executed)

Here is the list of related settings :

Setting	Default	Description
BLACKLIST_COUNTRY		List of 2 letters country code to blacklist.
WHITELIST_COUNTRY		List of 2 letters country code to whitelist.

Using both country blacklist and whitelist at the same time makes no sense. If you do, please note that only the whitelist will be executed.

Authentication

Auth basic

You can quickly protect sensitive resources like the admin area for example, by requiring HTTP basic authentication. Here is the list of related settings :

Setting	Default	Description
USE_AUTH_BASIC	no	When set to yes HTTP auth basic will be enabled.
AUTH_BASIC_LOCATION	sitewide	Location (URL) of the sensitive resource. Use special value sitewide to enable everywhere.
AUTH_BASIC_USER	changeme	The username required.
AUTH_BASIC_PASSWORD	changeme	The password required.
AUTH_BASIC_TEXT	Restricted area	Text to display in the auth prompt.

Auth request

You can deploy complex authentication (e.g. SSO), by using the auth request settings (see here for more information on the feature). Please note that you will find Authelia and Authentik examples in the repository.

Auth request settings are related to reverse proxy rules.

Setting	Default	Context	Multiple	Description
REVERSE_PROXY_AUTH_REQUEST		multisite	yes	Enable authentication using an external provider (value of auth_request directive).
REVERSE_PROXY_AUTH_REQUEST_SIGNIN_URL		multisite	yes	Redirect clients to sign-in URL when using REVERSE_PROXY_AUTH_REQUEST (used when auth_request call returned 401).
REVERSE_PROXY_AUTH_REQUEST_SET		multisite	yes	List of variables to set from the authentication provider, separated with ; (values of auth_request_set directives).