DWiki has a general attitude about security: it really distrusts incoming requests, it somewhat distrusts itself, but it has a rational trust of the people creating DWiki templates and pages. DWiki will try to save people from accidental mistakes, but doesn't bother with things that are just half-hearted attempts to stop people from deliberately sidestepping security restrictions. Moral: don't let people write DWiki pages unless you trust them.
Some knowledge of the ProcessingModel and the ConfigurationFile (and what can be set there) may be helpful for the rest of this discussion.
DWiki itself is written in Python (a lot of Python). This means that unless there is a gross implementation error in the Python interpreter, it is secure from simple problems such as buffer overruns. While DWiki uses some components from the standard Python libraries, they too are well-tested and believed to be entirely safe.
Because it is quite careful at multiple levels about how it handles requests, hostile HTTP requests should not be able to trick DWiki into serving anything from outside the page directory (or the comments directory, or the static content directory). InvalidPageNames discusses things it won't serve even inside them.
DWiki doesn't attempt to stop insiders from using DWiki to serve 'bad' content, ultimately because there are so many ways a malicious insider can do that. ChrisSiebenmann feels that it is better to be honest about not making any attempt rather than making an attempt and causing people to put more trust in it than it warrants.
If run as a CGI-BIN, DWiki should not be run with a UID that has any special access to restricted files. But then, no CGI-BIN should be run that way.
DWiki has some degree of optional Authentication, but it is no stronger than the usual run of the mill login and password on other web sites. Really sensitive content is probably best not served from a web server that the public (whatever that means to you) can access.
What people can do with the ability to write DWikiText in DWiki pages is somewhat less powerful than what they can do with the ability to write DWiki templates. Similarly, errors in DWikiText are considered far less fatal than errors in templates; DWikiText errors just result in funny-looking pages, while template errors result in terse web error pages.
Thus: while it's safe to let people write DWiki pages in general, you probably want to restrict (at least somewhat) who can write or modify your templates. Plus, your templates (being, you know, templates) shouldn't need modification all that often. People can create and modify pages all the time.
Internally, DWiki tries to operate in a relatively 'security conservative' fashion. For example, the frontend rejects clearly invalid things without passing them through to the DWiki core, because the core has a lot more power than the frontend so a mistake has larger ramifications.
DWiki also is deliberately structured so as to give itself as little power as possible.
DWiki can hit a number of internal problems while processing a request; for example, a template that's called for might be missing. When this happens, DWiki aborts processing the entire request, throwing an error all the way back to the front end, which generates a terse error page about the situation.
This may be abrupt ... but it is safe.
DWiki reads only a few files: the ConfigurationFile, the global-authseed-file file, the authfile password file, and things under the page, template, RCS, static files, and comments directories (if those are configured on).
Except for the password file, the DWiki core only accesses files through a simple storage layer abstraction, which provides 'storage pools' to the rest of DWiki. Each storage pool confines all file requests to relative paths under the pool's root, explicitly ruling out InvalidPageNames when retrieving files for the rest of DWiki.
The storage layer has no general file writing capabilities. The only interface it has for writing files is specifically designed for comments, using a specific naming and storage scheme. And only the comments directory uses a storage pool that supports this abstraction.
Unlike some web servers (eg, Apache), DWiki takes no special care to not follow symbolic links that point outside one of its storage pool directory roots. If you put such a symbolic link into a storage pool area, DWiki assumes that you know what you're doing.
This is deliberate. Attempting to duplicate the kernel's
function in user space is inevitably very complicated (and prone to
surprising races). Rather than run the risk of making a mistake in the
amount of code required, DWiki is honest about the whole situation.
DWiki refuses to serve any request that is not under
rooturl. Anything under
staticurl must be a static request
and is served only as such.
In addition to dynamic DWiki pages, DWiki can serve static content via
staticdir ConfigurationFile directive. Since DWiki's goals for
serving static content are very modest (CSS files, images, etc), DWiki
refuses requests for static directories. As mentioned in
ProcessingModel, static content is served by the frontend, thereby
keeping the amount of code involved in the process down.
In addition, DWiki rejects any request for static content that is not in the default 'normal' view.