Safe Modes

Asciidoctor provides security levels that control the read and write access of attributes, include directives, macros, and scripts while a document is processing. Each level includes the restrictions enabled in the prior security level.

Security assumptions

Asciidoctor’s safe modes are primarily focused on what the processor is permitted to do. The safe modes do not provide a comprehensive security framework. In particular, there’s no safe mode that restricts the kind of content the author can pass through to the output document. In other words, the safe mode setting does not provide a way to santiize the output.

Asciidoctor performs sensible escaping to allow an author to safely input text, but does not limit the content that can be included in the output using passthrough blocks or custom substitutions. The reason for this policy is that we assume the document will be passed through a sanitizer if the HTML must be embedded directly into a web page, precisely what GitHub and GitLab do. This postprocessing (which could be done using a postprocessor extension) is better handled by a separate tool since. There are many permutations to consider and only a separate tool would know which restrictions to apply for a given situation.

The safe mode can be set from the CLI and the API. You can also enable or disable content based on the current safe mode.

UNSAFE

The UNSAFE safe mode level disables any security features enforced by Asciidoctor. Ruby is still subject to its own restrictions.

This is the default safe mode for the CLI. Its integer value is 0.

SAFE

The SAFE safe mode level prevents access to files which reside outside of the parent directory of the source file. Include directives (include::[]) are enabled, but paths to include files must be within the parent directory. This mode allows assets (such as the stylesheet) to be embedded in the document.

Its integer value is 1.

SERVER

The SERVER safe mode level disallows the document from setting attributes that would affect conversion of the document. This level trims docfile to its relative path and prevents the document from:

  • setting source-highlighter, doctype, docinfo and backend

  • seeing docdir (as it can reveal information about the host filesystem)

It allows icons and linkcss.

Its integer value is 10.

SECURE

The SECURE safe mode level disallows the document from attempting to read files from the file system and including their contents into the document. Additionally, it:

  • disables icons

  • disables include directives (include::[])

  • data can not be retrieved from URIs

  • prevents access to stylesheets and JavaScripts

  • sets the backend to html5

  • disables docinfo files

  • disables data-uri

  • disables interactive (opts=interactive) and inline (opts=inline) modes for SVGs

  • disables docdir and docfile (as these can reveal information about the host filesystem)

  • disables source highlighting

Asciidoctor extensions may still embed content into the document depending whether they honor the safe mode setting.

This is the default safe mode for the API. Its integer value is 20.

GitHub processes AsciiDoc files using the SECURE mode.