Libmodsecurity is one component of the ModSecurity v3 project. The library codebase serves as an interface to ModSecurity Connectors taking in web traffic and applying traditional ModSecurity processing. In general, it provides the capability to load/interpret rules written in the ModSecurity SecRules format and apply them to HTTP content provided by your application via Connectors.

If you are looking for ModSecurity for Apache (aka ModSecurity v2.x), it is still under maintenance and available: here.

What is the difference between this project and the old ModSecurity (v2.x.x)?

• All Apache dependencies have been removed
• Higher performance
• New features
• New architecture

Libmodsecurity is a complete rewrite of the ModSecurity platform. When it was first devised the ModSecurity project started as just an Apache module. Over time the project has been extended, due to popular demand, to support other platforms including (but not limited to) Nginx and IIS. In order to provide for the growing demand for additional platform support, it has became necessary to remove the Apache dependencies underlying this project, making it more platform independent.

As a result of this goal we have rearchitected Libmodsecurity such that it is no longer dependent on the Apache web server (both at compilation and during runtime). One side effect of this is that across all platforms users can expect increased performance. Additionally, we have taken this opportunity to lay the groundwork for some new features that users have been long seeking. For example we are looking to natively support auditlogs in the JSON format, along with a host of other functionality in future versions.

It is no longer just a module.

The 'ModSecurity' branch no longer contains the traditional module logic (for Nginx, Apache, and IIS) that has traditionally been packaged all together. Instead, this branch only contains the library portion (libmodsecurity) for this project. This library is consumed by what we have termed 'Connectors' these connectors will interface with your webserver and provide the library with a common format that it understands. Each of these connectors is maintained as a separate GitHub project. For instance, the Nginx connector is supplied by the ModSecurity-nginx project (https://github.com/owasp-modsecurity/ModSecurity-nginx).

Keeping these connectors separated allows each project to have different release cycles, issues and development trees. Additionally, it means that when you install ModSecurity v3 you only get exactly what you need, no extras you won't be using.

Compilation

Before starting the compilation process, make sure that all required dependencies are installed.
See the Dependencies and Git submodules section for further information.

After compilation, make sure that there are no issues on your build/platform.
We strongly recommend running the unit tests and regression tests. These test utilities are located in the tests/ subfolder.

As a dynamic library, libmodsecurity must be installed in a location where your operating system can find dynamic libraries.

Unix (Linux, macOS, FreeBSD, …)

On Unix-like systems, the project uses autotools for the compilation process.

If you are working with a git checkout, make sure to clone the repository recursively or initialize all submodules before building.
See also the Git submodules section.

git clone https://github.com/owasp-modsecurity/ModSecurity ModSecurity
cd ModSecurity

This repository uses git submodules. After cloning, make sure to initialize and fetch all submodules:

git submodule update --init --recursive

You can verify that all submodules are properly initialized with:

git submodule status

Submodules that are correctly initialized show a commit hash. A leading - indicates that the submodule has not been initialized.

You can then start the build process:

./build.sh
./configure
make
sudo make install

Details on distribution-specific builds can be found in our Wiki: Compilation Recipes

Windows

Windows build information can be found here.

Dependencies

• This library is written in C++ using the C++17 standard.
• It uses Flex and Bison (Yacc) to produce the “Sec Rules Language” parser.
• Mandatory dependencies include YAJL, as ModSecurity uses JSON for logging and its testing framework.
• libXML2 (optional) is used for parsing XML requests.

Regular expression engine (PCRE2 / PCRE)

• Regular expression processing in SecRules is implemented via the Regex utility (src/utils/regex.*).

• By default, ModSecurity uses PCRE2 for regex handling.

• This is used by operators such as @rx, @rxGlobal, and @verifyCC.

• Build-time behavior:

  • Default: PCRE2 is detected and used.
  • Fallback: legacy PCRE can be used if --with-pcre is explicitly provided (WITH_PCRE).

• In other words, current builds expect PCRE2 unless explicitly configured otherwise.

• @rx and @rxGlobal compile patterns with DOTALL | MULTILINE by default: DOTALL lets . match newlines, and MULTILINE lets ^/$ anchor at every internal line break rather than only at the start/end of the whole subject. Pass --enable-regex-dollar-endonly=yes to compile them with DOTALL | DOLLAR_ENDONLY instead: without MULTILINE, ^/$ anchor only at the start/end of the whole subject, and DOLLAR_ENDONLY further restricts $ to match only there rather than also just before a trailing newline. DOTALL is unchanged either way, so patterns can still match across internal line breaks via .. This matches ModSecurity v2's @rx behavior. The flag is disabled by default; see issue #3295.

All other dependencies are related to operators specified within SecRules or configuration directives and may not be required for compilation.

Operator-related dependencies

• libinjection is required for the operators @detectXSS and @detectSQL.
• curl is required for the directive SecRemoteRules.

If those libraries are missing, ModSecurity will be compiled without support for the respective operators or directives.

Git-submodules

The repository includes the following submodules: