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OWASP CRS Docker Image

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What is the OWASP CRS

OWASP CRS is a set of generic attack detection rules for use with ModSecurity or compatible web application firewalls. ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx.

Supported Tags

Stable Tags

Stable Tags are composed of:

  • CRS version, in the fromat <major>[.<minor>[.<patch]]
  • web server variant
  • OS variant (optional)
  • date, in the format YYYYMMDDHHMM

The stable tag format is <CRS version>-<web server>[-<os>]-<date>. Examples:

  • 4-nginx-202401121309
  • 4.0-apache-alpine-202401121309
  • 4.0.0-openresty-alpine-fat-202401121309

Rolling Tags

Rolling tags are updated whenever a new stable tag release occurs. Rolling tags can be practical but should not be used in production.

Rolling Tags are composed of:

  • web server variant
  • OS variant (optional)

The stable tag format is <web server>[-<os>]. Examples:

  • nginx
  • apache-alpine
  • openresty-alpine-fat

OS Variants

  • nginx – latest stable ModSecurity v3 on Nginx 1.26.0 official stable base image, and latest stable OWASP CRS 4.2.0
  • Openresty - last stable ModSecurity v3 on OpenResty 1.25.3.1 official stable base image, and latest stable OWASP CRS 4.2.0
  • Apache httpd – last stable ModSecurity v2 on Apache 2.4.59 official stable base image, and latest stable OWASP CRS 4.2.0

Notes regarding Openresty version of this image

We currently only provide a version of the Openresty image based on Alpine Linux. The Dockerfile for Openresty resides in the docker-openresty repository.

Supported architectures

Our builds are based on the official Apache httpd, nginx and Openresty images, which means we can only support the architectures they support.

We currently provide images for the following architectures:

  • linux/amd64
  • linux/arm/v7
  • linux/arm64/v8
  • linux/i386

Building

We require a version of buildx >= v0.9.1. Visit the official documentation for instructions on installing and upgrading buildx. You can check which version you have using:

docker buildx version
github.com/docker/buildx v0.9.1 ed00243a0ce2a0aee75311b06e32d33b44729689

If you want to see the targets of the build, use:

docker buildx bake -f ./docker-bake.hcl --print

To build for any platforms of your choosing, just use this example:

docker buildx create --use --platform linux/amd64,linux/i386,linux/arm64,linux/arm/v7
docker buildx bake -f docker-bake.hcl

To build a specific target for a single platform only (replace target and platform strings in the example with the your choices):

docker buildx bake -f docker-bake.hcl --set "*.platform=linux/amd64" nginx-alpine

Notes regarding Openresty version of the image

Openresty image builds currently support only these architectures:

  • linux/amd64
  • linux/arm64

Container Health Checks

🆕 We add healthchecks to the images, so that containers return HTTP status code 200 from the /healthz endpoint. When a container has a healthcheck specified, it has a health status in addition to its normal status. This status is initially starting. Whenever a health check passes, it becomes healthy (whatever state it was previously in). After a certain number of consecutive failures, it becomes unhealthy. See https://docs.docker.com/engine/reference/builder/#healthcheck for more information.

CRS Versions

Hey, I used some specific git version with the containers? What happened?

You can achieve the same results just by getting any version you want, and using docker volumes. See this example:

git clone https://github.com/coreruleset/coreruleset.git myrules
cd myrules
git checkout ac2a0d1
docker run -p 8080:8080 -ti -e PARANOIA=4 -v rules:/opt/owasp-crs/rules:ro --rm owasp/modsecurity-crs

Quick reference

What is ModSecurity

ModSecurity is an open source, cross platform Web Application Firewall (WAF) engine for Apache, IIS and Nginx. It has a robust event-based programming language which provides protection from a range of attacks against web applications and allows for HTTP traffic monitoring, logging and real-time analysis.

Nginx based images breaking change

⚠️ WARNING
Nginx based images are now based on upstream nginx. This changed the way the config file for nginx is generated.

If using the Nginx environment variables is not enough for your use case, you can mount your own nginx.conf file as the new template for generating the base config.

An example can be seen in the docker-compose file.

💬 What happens if I want to make changes in a different file, like /etc/nginx/conf.d/default.conf? You mount your local file, e.g. nginx/default.conf as the new template: /etc/nginx/templates/conf.d/default.conf.template. You can do this similarly with other files. Files in the templates directory will be copied and subdirectories will be preserved.

Both nginx and httpd containers now run with an unprivileged user. This means that we cannot bind to ports below 1024, so you might need to correct your PORT and SSL_PORT settings. Now the defaults for both nginx and httpd are 8080 and 8443.

Common ENV Variables

These variables are common to image variants and will set defaults based on the image name.

Name Description httpd default nginx / Openresty default (if different)
ACCESSLOG Location of the custom log file /var/log/apache2/access.log /var/log/nginx/access.log
BACKEND Partial URL for the remote server of the ProxyPass (httpd) and proxy_pass (nginx) directives http://localhost:80 -
ERRORLOG Location of the error log file /proc/self/fd/2 -
LOGLEVEL Minimum level for log messages to be logged to the error log warn -
METRICS_ALLOW_FROM A single range of IP adresses that can access the metrics 127.0.0.0/255.0.0.0 ::1/128 127.0.0.0/24
METRICS_DENY_FROM A range of IP adresses that cannot access the metrics All all
METRICSLOG Location of metrics log file /dev/null -
PROXY_SSL_CERT A string indicating the path to the PEM-encoded X.509 certificate data file or token identifier of the proxied server /usr/local/apache2/conf/proxy.crt /etc/nginx/conf/proxy.crt / /usr/local/openresty/nginx/conf/proxy.crt
PROXY_SSL_CERT_KEY A string indicating the path to the PEM-encoded private key file of the proxied server /usr/local/apache2/conf/proxy.key /etc/nginx/conf/proxy.key / /usr/local/openresty/nginx/conf/proxy.key
PROXY_SSL_CIPHERS A string indicating the cipher suite to connect to the backend via TLS "ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384" -
PROXY_SSL_PROTOCOLS TLS protocols to enable for the connection to the backend "all -SSLv3 -TLSv1 -TLSv1.1" TTLSv1.2 TLSv1.3
PROXY_SSL SSL Proxy Engine Operation Switch off -
PROXY_SSL_VERIFY A string value indicating the type of proxy server Certificate verification none off
PROXY_TIMEOUT Number of seconds for proxied requests to time out 60 60s
SERVER_NAME The server name localhost -
SSL_CERT A string indicating the path to the PEM-encoded X.509 certificate data file or token identifier of the proxied server /usr/local/apache2/conf/server.crt /etc/nginx/conf/server.crt / /usr/local/openresty/nginx/conf/server.crt
SSL_CERT_KEY A string indicating the path to the PEM-encoded private key file of the proxied server /usr/local/apache2/conf/server.key /etc/nginx/conf/server.key / /usr/local/openresty/nginx/conf/server.key
SSL_CIPHERS A string indicating the cipher suite for incoming TLS connections "ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384" -
SSL_OCSP_STAPLING Enable / disable OCSP stapling On on
SSL_PROTOCOLS TLS protocols to enable for the connection to the backend "all -SSLv3 -TLSv1 -TLSv1.1" TTLSv1.2 TLSv1.3

Apache ENV Variables

Name Description
APACHE_ALWAYS_TLS_REDIRECT A string value indicating if http should redirect to https (Allowed values: on, off. Default: off)
APACHE_ERRORLOG_FORMAT A string value indicating the ErrorLogFormat that Apache should use. (Default: '"[%{u}t] [%-m:%l] [pid %P:tid %T] %7F: %E: [client\ %a] %M% ,\ referer\ %{Referer}i"'
APACHE_LOGFORMAT A string value indicating the LogFormat that apache should use. (Default: '"%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-agent}i\""' (combined). Tip: use single quotes outside your double quoted format string.) ⚠️ Do not add a `
APACHE_METRICS_LOGFORMAT A string value indicating the LogFormat that the additional log apache metrics should use. (Default:'"%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-agent}i""' (combined). Tip: use single quotes outside your double quoted format string.) ⚠️ Do not add a `
BACKEND_WS A string indicating the IP/URL of the WebSocket service (Default: ws://localhost:8081)
H2_PROTOCOLS A string value indicating the protocols supported by the HTTP2 module (Default: h2 http/1.1)
MUTEX Configure mutex and lock file directory for all specified mutexes (see Mutex) (Default: default)
PORT An int value indicating the port where the webserver is listening to
PROXY_ERROR_OVERRIDE A string indicating that errors from the backend services should be overridden by this proxy server (see ProxyErrorOverride directive). (Allowed values: on, off. Default: on)
PROXY_PRESERVE_HOST A string indicating the use of incoming Host HTTP request header for proxy request (Default: on)
PROXY_SSL_CA_CERT A string indicating the path to the PEM-encoded list of accepted CA certificates for the proxied server (Default: /etc/ssl/certs/ca-certificates.ca)
PROXY_SSL_CHECK_PEER_NAME A string indicating if the host name checking for remote server certificates is to be enabled (Default: on)
REMOTEIP_INT_PROXY A string indicating the client intranet IP addresses trusted to present the RemoteIPHeader value (Default: 10.1.0.0/16)
REQ_HEADER_FORWARDED_PROTO A string indicating the transfer protocol of the initial request (Default: https)
SERVER_ADMIN A string value indicating the address where problems with the server should be e-mailed (Default: root@localhost)
SERVER_SIGNATURE A string value configuring the footer on server-generated documents (Allowed values: On, Off, EMail. Default: Off)
SERVER_TOKENS Option defining the server information presented to clients in the Server HTTP response header. Also see MODSEC_SERVER_SIGNATURE. (Allowed values: Full, Prod[uctOnly], Major, Minor, Min[imal], OS. Default: Full).
SSL_ENGINE A string indicating the SSL Engine Operation Switch (Default: on)
SSL_HONOR_CIPHER_ORDER A string indicating if the server should honor the cipher list provided by the client (Allowed values: on, off. Default: off)
SSL_PORT Port number where the SSL enabled webserver is listening
SSL_SESSION_TICKETS A string to enable or disable the use of TLS session tickets (RFC 5077). (Default: off)
TIMEOUT Number of seconds before receiving and sending timeout (Default: 60)
WORKER_CONNECTIONS Maximum number of MPM request worker processes (Default: 400)

Note

Apache access and metric logs can be disabled by exporting the nologging=1 environment variable, or using ACCESSLOG=/dev/null and METRICSLOG=/dev/null.

Nginx ENV Variables

Name Description
DNS_SERVER A string indicating the name servers used to resolve names of upstream servers into addresses. For localhost backend this value should not be defined (Default: not defined)
KEEPALIVE_TIMEOUT Number of seconds for a keep-alive client connection to stay open on the server side (Default: 60s)
NGINX_ALWAYS_TLS_REDIRECT A string value indicating if http should redirect to https (Allowed values: on, off. Default: off)
PORT An int value indicating the port where the webserver is listening to
PROXY_SSL_VERIFY_DEPTH An integer value indicating the verification depth for the client certificate chain (Default: 1)
REAL_IP_HEADER Name of the header containing the real IP value(s) (Default: X-REAL-IP). See real_ip_header
REAL_IP_PROXY_HEADER Name of the header containing $remote_addr to be passed to proxy (Default: X-REAL-IP). See proxy_set_header
REAL_IP_RECURSIVE A string value indicating whether to use recursive reaplacement on addresses in REAL_IP_HEADER (Allowed values: on, off. Default: on). See real_ip_recursive
SERVER_TOKENS A boolean value for enabling / disabling emission of server identifying information in the Server HTTP response header and on error pages. (Allowed values: on, off, build. Default: off).
SET_REAL_IP_FROM A string of comma separated IP, CIDR, or UNIX domain socket addresses that are trusted to replace addresses in REAL_IP_HEADER (Default: 127.0.0.1). See set_real_ip_from
SSL_DH_BITS A numeric value indicating the size (in bits) to use for the generated DH-params file (Default 2048)
SSL_PORT Port number where the SSL enabled webserver is listening
SSL_PREFER_CIPHERS A string value indicating if the server ciphers should be preferred over client ciphers when using the SSLv3 and TLS protocols (Allowed values: on, off. Default: off)
SSL_VERIFY A string value indicating if the client certificates should be verified (Allowed values: on, off. Default: off)
SSL_VERIFY_DEPTH An integer value indicating the verification depth for the client certificate chain (Default: 1)
WORKER_CONNECTIONS Maximum number of simultaneous connections that can be opened by a worker process (Default: 1024)

Openresty ENV Variables

Openresty uses the same environment variables as the nginx version.

ModSecurity ENV Variables

All these variables impact in configuration directives in the modsecurity engine running inside the container. The reference manual has the extended documentation, and for your reference we list the specific directive we change when you modify the ENV variables for the container.

Name Description
MODSEC_ARGUMENT_SEPARATOR A character to use as the separator for application/x-www-form-urlencoded content. (Default: &). ⚠️ Do not touch unless you really know what you are doing. See SecArgumentSeparator
MODSEC_ARGUMENTS_LIMIT An integer indicating the maximum number of arguments that can be processed before setting the REQBODY_ERROR variable (Default 1000). See SecArgumentsLimit
MODSEC_AUDIT_ENGINE A string used to configure the audit engine, which logs complete transactions (Default: RelevantOnly). Accepted values: On, Off, RelevantOnly. See SecAuditEngine for additional information.
MODSEC_AUDIT_LOG A string indicating the path to the main audit log file or the concurrent logging index file (Default: /dev/stdout)
MODSEC_AUDIT_LOG_FORMAT A string indicating the output format of the AuditLogs (Default: JSON). Accepted values: JSON, Native. See SecAuditLogFormat for additional information.
MODSEC_AUDIT_LOG_PARTS A string that defines which parts of each transaction are going to be recorded in the audit log (Default: 'ABIJDEFHZ'). See SecAuditLogParts for the accepted values.
MODSEC_AUDIT_LOG_RELEVANT_STATUS A regular expression string that defines the http error codes that are relevant for audit logging (Default: `"^(?:5
MODSEC_AUDIT_LOG_TYPE A string indicating the type of audit logging mechanism to be used (Default: Serial). Accepted values: Serial, Concurrent (HTTPS works only on Nginx - v3). See SecAuditLogType for additional information.
MODSEC_COOKIE_FORMAT The cookie format used (Default: 0 use Netscape cookies) ⚠️ Do not touch unless you really know what you are doing. See SecCookieFormat.
MODSEC_AUDIT_STORAGE_DIR A string indicating the directory where concurrent audit log entries are to be stored (Default: /var/log/modsecurity/audit/)
MODSEC_DATA_DIR A string indicating the path where persistent data (e.g., IP address data, session data, and so on) is to be stored (Default: /tmp/modsecurity/data)
MODSEC_DEBUG_LOG A string indicating the path to the ModSecurity debug log file (Default: /dev/null)
MODSEC_DEBUG_LOGLEVEL An integer indicating the verboseness of the debug log data (Default: 0). Accepted values: 0 - 9. See SecDebugLogLevel.
MODSEC_DEFAULT_PHASE1_ACTION ModSecurity string with the contents for the default action in phase 1 (Default: 'phase:1,log,auditlog,pass,tag:\'\${MODSEC_TAG}\'')
MODSEC_DEFAULT_PHASE2_ACTION ModSecurity string with the contents for the default action in phase 2 (Default: 'phase:2,log,auditlog,pass,tag:\'\${MODSEC_TAG}\'')
MODSEC_DISABLE_BACKEND_COMPRESSION A string indicating whether or not to disable backend compression (Default: On). Allowed values: On, Off. See SecDisableBackendCompression for more. Only supported in ModSecurity 2.x, will have not effect on 3.x
MODSEC_PCRE_MATCH_LIMIT An integer value indicating the limit for the number of internal executions in the PCRE function (Default: 100000) (Only valid for Apache - v2). See SecPcreMatchLimit
MODSEC_PCRE_MATCH_LIMIT_RECURSION An integer value indicating the limit for the depth of recursion when calling PCRE function (Default: 100000)
MODSEC_REQ_BODY_ACCESS A string value allowing ModSecurity to access request bodies (Default: On). Allowed values: On, Off. See SecRequestBodyAccess for more information.
MODSEC_REQ_BODY_JSON_DEPTH_LIMIT An integer value indicating the maximun JSON request depth (Default: 512). See SecRequestBodyJsonDepthLimit for additional information.
MODSEC_REQ_BODY_LIMIT_ACTION A string value for the action when SecRequestBodyLimit is reached (Default: Reject). Accepted values: Reject, ProcessPartial. See SecRequestBodyLimitAction for additional information.
MODSEC_REQ_BODY_LIMIT An integer value indicating the maximum request body size accepted for buffering (Default: 13107200). See SecRequestBodyLimit for additional information.
MODSEC_REQ_BODY_NOFILES_LIMIT An integer indicating the maximum request body size ModSecurity will accept for buffering (Default: 131072). See SecRequestBodyNoFilesLimit for more information.
MODSEC_RESP_BODY_ACCESS A string value allowing ModSecurity to access response bodies (Default: On). Allowed values: On, Off. See SecResponseBodyAccess for more information.
MODSEC_RESP_BODY_LIMIT_ACTION A string value for the action when SecResponseBodyLimit is reached (Default: ProcessPartial). Accepted values: Reject, ProcessPartial. See SecResponseBodyLimitAction for additional information.
MODSEC_RESP_BODY_LIMIT An integer value indicating the maximum response body size accepted for buffering (Default: 1048576)
MODSEC_RESP_BODY_MIMETYPE A string with the list of mime types that will be analyzed in the response (Default: 'text/plain text/html text/xml'). You might consider adding application/json documented here.
MODSEC_RULE_ENGINE A string value enabling ModSecurity itself (Default: On). Accepted values: On, Off, DetectionOnly. See SecRuleEngine for additional information.
MODSEC_SERVER_SIGNATURE Sets the directive SecServerSignature and instructs ModSecurity to change the data presented in the "Server:" response header token when Apache ServerTokens directive is set to Full. Also see Apache SERVER_TOKENS. Only supported in ModSecurity 2.x, will have not effect on 3.x. (Default: Apache).
MODSEC_STATUS_ENGINE A string used to configure the status engine, which sends statistical information (Default: Off). Accepted values: On, Off. See SecStatusEngine for additional information.
MODSEC_TAG A string indicating the default tag action, which will be inherited by the rules in the same configuration context (Default: modsecurity)
MODSEC_TMP_DIR A string indicating the path where temporary files will be created (Default: /tmp/modsecurity/tmp)
MODSEC_TMP_SAVE_UPLOADED_FILES A string indicating if temporary uploaded files are saved (Default: On) (only relevant in Apache - ModSecurity v2)
MODSEC_UNICODE_MAPPING The unicode Code Point to use form the default file(Default: 20127). See SecUnicodeMapFile
MODSEC_UPLOAD_DIR A string indicating the path where intercepted files will be stored (Default: /tmp/modsecurity/upload)
MODSEC_UPLOAD_FILE_MODE (Default: 0600)
MODSEC_UPLOAD_KEEP_FILES Configures whether or not the intercepted files will be kept after transaction is processed. (Default: RelevantOnly on Apache, Off on nginx) Accepted values: On, Off, RelevantOnly (only modsec2). See SecUploadKeepFiles and libmodsecurity3

CRS specific

Name Description
ALLOWED_HTTP_VERSIONS A string indicating the allowed_http_versions (Default: HTTP/1.0 HTTP/1.1 HTTP/2 HTTP/2.0)
ALLOWED_METHODS A string indicating the allowed_methods (Default: GET HEAD POST OPTIONS)
ALLOWED_REQUEST_CONTENT_TYPE A string indicating the allowed_request_content_type (Default: |application/x-www-form-urlencoded| |multipart/form-data| |multipart/related| |text/xml| |application/xml| |application/soap+xml| |application/json| |application/cloudevents+json| |application/cloudevents-batch+json|)
ALLOWED_REQUEST_CONTENT_TYPE_CHARSET A string indicating the allowed_request_content_type_charset (Default: utf-8|iso-8859-1|iso-8859-15|windows-1252)
ANOMALY_INBOUND An integer indicating the inbound_anomaly_score_threshold (Default: 5)
ANOMALY_OUTBOUND An integer indicating the outbound_anomaly_score_threshold (Default: 4)
ARG_LENGTH An integer indicating the arg_length (Default: unlimited)
ARG_NAME_LENGTH An integer indicating the arg_name_length (Default: unlimited)
BLOCKING_PARANOIA (:new: Replaces PARANOIA in CRSv4) An integer indicating the paranoia level (Default: 1)
COMBINED_FILE_SIZES An integer indicating the combined_file_sizes (Default: unlimited)
CRS_DISABLE_PLUGINS A boolean indicating whether plugins will be disabled (Only from v4 and up. Default: 0)
CRS_ENABLE_TEST_MARKER A boolean indicating whether to write test markers to the log file (Used for running the CRS test suite. Default: 0)
DETECTION_PARANOIA (:new: Replaces EXECUTING_PARANOIA in CRSv4) An integer indicating the detection_paranoia_level (Default: BLOCKING_PARANOIA)
ENFORCE_BODYPROC_URLENCODED A boolean indicating the enforce_bodyproc_urlencoded (Default: 0)
EXECUTING_PARANOIA An integer indicating the executing_paranoia_level (Default: PARANOIA)
MANUAL_MODE A boolean indicating that you are providing your own crs-setup.conf file mounted as volume. (Default: 0). ⚠️ None of the following variables are used if you set it to 1.
MAX_FILE_SIZE An integer indicating the max_file_size (Default: unlimited)
MAX_NUM_ARGS An integer indicating the max_num_args (Default: unlimited)
PARANOIA An integer indicating the paranoia level (Default: 1)
RESTRICTED_EXTENSIONS A string indicating the restricted_extensions (Default: .asa/ .asax/ .ascx/ .axd/ .backup/ .bak/ .bat/ .cdx/ .cer/ .cfg/ .cmd/ .com/ .config/ .conf/ .cs/ .csproj/ .csr/ .dat/ .db/ .dbf/ .dll/ .dos/ .htr/ .htw/ .ida/ .idc/ .idq/ .inc/ .ini/ .key/ .licx/ .lnk/ .log/ .mdb/ .old/ .pass/ .pdb/ .pol/ .printer/ .pwd/ .rdb/ .resources/ .resx/ .sql/ .swp/ .sys/ .vb/ .vbs/ .vbproj/ .vsdisco/ .webinfo/ .xsd/ .xsx/)
RESTRICTED_HEADERS A string indicating the restricted_headers (Default: /accept-charset/ /content-encoding/ /proxy/ /lock-token/ /content-range/ /if/)
STATIC_EXTENSIONS A string indicating the static_extensions (Default: /.jpg/ /.jpeg/ /.png/ /.gif/ /.js/ /.css/ /.ico/ /.svg/ /.webp/)
TOTAL_ARG_LENGTH An integer indicating the total_arg_length (Default: unlimited)
VALIDATE_UTF8_ENCODING A boolean indicating the crs_validate_utf8_encoding (Default: 0)

TLS/HTTPS

Important

The default configuration generates a self signed certificate on first run. To use your own certificates (recommended) COPY or mount (-v) your server.crt and server.key into /usr/local/apache2/conf/ or /etc/nginx/conf/. Remember to publish the HTTPS port when running the image.

docker build -t my-modsec .
docker run -p 8443:8443 my-modsec

TLS is configured on port 8443 and enabled by default.

We use sane intermediate defaults taken from the Mozilla SSL config tool. Please review the defaults and choose the ones that best match your needs.

You can set the *_ALWAYS_TLS_REDIRECT environment variables to always redirect from http to https.

Proxy Configuration

The owasp/modsecurity-crs container images in their default configuration (i.e., without manual changes to / overrides of configuration files) act as reverse proxies and require a running backend at the address specified through the BACKEND environment variable.

Important

Make sure to set the BACKEND variable to an address where a web server is listening. Otherwise nothing useful will happen when you send requests to the owasp/modsecurity-crs container (at least not with the default configurational).

ModSecurity is often used in a reverse proxy setup with the following porperties:

  • reverse proxy acts as public end point
  • reverse proxy performs TLS termination (necessary for ModSecurity to inspect content)
  • ModSecurity runs on the reverse proxy to filter traffic
  • only benign traffic is passed to the backend

This allows one to use ModSecurity without modifying the webserver hosting the underlying application and also protects web servers that ModSecurity cannot currently be embedd into.

Tips:

  • the application web server (the one receiving traffic from the reverse proxy) should not listen on a public interface. Only the reverse proxy should be exposed to the public. With Docker, this could mean setting up a network for both containers and only exposing the reverse proxy with -p 8080:8080, for example. docker compose takes care of this automatically. See the docker-compose.yaml for an example setup.
docker build -t my-modsec . -f
docker run -p 8080:8080 -e BACKEND=http://example.com my-modsec

ServerName

It is often convenient to set your server name (set to localhost by defualt). To do this simply use the SERVER_NAME environment variable.

docker build -t modsec .
docker run -p 8080:8080 -e SERVER_NAME=myhost my-modsec

ModSecurity CRS Tuning

There are two possible ways to pass ModSecurity CRS tuning rules to the container:

  • To map the ModSecurity tuning file(s) via volumes into the container during the run command
  • To copy the ModSecurity tuning file(s) into the created container and then start the container

Map ModSecurity tuning file via volume

docker run -dti --rm \
   -p 8080:8080 \
   -v /path/to/REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf:/etc/modsecurity.d/owasp-crs/rules/REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf \
   -v /path/to/RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf:/etc/modsecurity.d/owasp-crs/rules/RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf \
   owasp/modsecurity-crs:apache

Copy ModSecurity tuning file into created container

This example can be helpful when no volume mounts are possible (some CI pipelines).

docker create -ti --name modseccrs \
   -p 8080:8080 \
   owasp/modsecurity-crs:apache

docker cp /path/to/RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf \
   modseccrs:/etc/modsecurity.d/owasp-crs/rules/RESPONSE-999-EXCLUSION-RULES-AFTER-CRS.conf

docker start modseccrs

Full docker run example of possible setup

The following example illustrates how to use docker run with some of the variables. It's purpose is illustration only and it should not be used to run a container in production.

Some important things to note:

  • Error and audit logs are enabled and mapped to files on the host, so that their contents are accessible and don't pollute the container filesystem. Docker requires these files to exist, otherwise they would be created as directories, hence the use of the touch ... commands.
  • For containers with read-only filesystems, the volumes might have to be specified differently, e.g., using tmpfs. Alternatively, if only one log output is required, the output could be redirected to stdout (/proc/self/fd/2).
  • The example expects a backend web server to be running at localhost:8081.
touch /tmp/host-fs-auditlog.log
touch /tmp/host-fs-errorlog.log
docker run \
   -dti \
   -p 8080:8080 \
   --rm \
   -v /tmp/host-fs-auditlog.log:/var/log/modsec_audit.log \
   -v /tmp/host-fs-errorlog.log:/var/log/modsec_error.log \
   -e MODSEC_AUDIT_ENGINE=on \
   -e MODSEC_AUDIT_LOG=/var/log/modsec_audit.log
   -e LOGLEVEL=warn \
   -e ERRORLOG=/var/log/modsec_error.log \
   -e PARANOIA=1 \
   -e EXECUTING_PARANOIA=2 \
   -e ENFORCE_BODYPROC_URLENCODED=1 \
   -e ANOMALY_INBOUND=10 \
   -e ANOMALY_OUTBOUND=5 \
   -e ALLOWED_METHODS="GET POST PUT" \
   -e ALLOWED_REQUEST_CONTENT_TYPE="text/xml|application/xml|text/plain" \
   -e ALLOWED_REQUEST_CONTENT_TYPE_CHARSET="utf-8|iso-8859-1" \
   -e ALLOWED_HTTP_VERSIONS="HTTP/1.1 HTTP/2 HTTP/2.0" \
   -e RESTRICTED_EXTENSIONS=".cmd/ .com/ .config/ .dll/" \
   -e RESTRICTED_HEADERS="/proxy/ /if/" \
   -e STATIC_EXTENSIONS="/.jpg/ /.jpeg/ /.png/ /.gif/" \
   -e MAX_NUM_ARGS=128 \
   -e ARG_NAME_LENGTH=50 \
   -e ARG_LENGTH=200 \
   -e TOTAL_ARG_LENGTH=6400 \
   -e MAX_FILE_SIZE=100000 \
   -e COMBINED_FILE_SIZES=1000000 \
   -e TIMEOUT=60 \
   -e SERVER_ADMIN=root@localhost \
   -e SERVER_NAME=localhost \
   -e PORT=8080 \
   -e MODSEC_RULE_ENGINE=on \
   -e MODSEC_REQ_BODY_ACCESS=on \
   -e MODSEC_REQ_BODY_LIMIT=13107200 \
   -e MODSEC_REQ_BODY_NOFILES_LIMIT=131072 \
   -e MODSEC_RESP_BODY_ACCESS=on \
   -e MODSEC_RESP_BODY_LIMIT=524288 \
   -e MODSEC_PCRE_MATCH_LIMIT=1000 \
   -e MODSEC_PCRE_MATCH_LIMIT_RECURSION=1000 \
   -e VALIDATE_UTF8_ENCODING=1 \
   -e CRS_ENABLE_TEST_MARKER=1 \
   -e BACKEND="http://localhost:8081" \
   owasp/modsecurity-crs:apache

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Official ModSecurity Docker + Core Rule Set (CRS) images

coreruleset.org

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