Apache Module mod_dav

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Description:	Distributed Authoring and Versioning (WebDAV) functionality
Status:	Extension
Module Identifier:	dav_module
Source File:	mod_dav.c

Summary

This module provides class 1 and class 2 WebDAV ('Web-based Distributed Authoring and Versioning') functionality for Apache. This extension to the HTTP protocol allows creating, moving, copying, and deleting resources and collections on a remote web server.

Topics

Enabling WebDAV
Security Issues
Complex Configurations

Enabling WebDAV

To enable mod_dav, add the following to a container in your httpd.conf file:

Dav On

This enables the DAV file system provider, which is implemented by the mod_dav_fs module. Therefore, that module must be compiled into the server or loaded at runtime using the LoadModule directive.

In addition, a location for the DAV lock database must be specified in the global section of your httpd.conf file using the DavLockDB directive:

DavLockDB /usr/local/apache2/var/DavLock

The directory containing the lock database file must be writable by the User and Group under which Apache is running.

You may wish to add a <Limit> clause inside the <Location> directive to limit access to DAV-enabled locations. If you want to set the maximum amount of bytes that a DAV client can send at one request, you have to use the LimitXMLRequestBody directive. The "normal" LimitRequestBody directive has no effect on DAV requests.

Full Example

DavLockDB /usr/local/apache2/var/DavLock <Location /foo> Order Allow,Deny Allow from all Dav On AuthType Basic AuthName DAV AuthUserFile user.passwd <LimitExcept GET OPTIONS> require user admin </LimitExcept> </Location>

mod_dav is a descendent of Greg Stein's mod_dav for Apache 1.3. More information about the module is available from that site.

Security Issues

Since DAV access methods allow remote clients to manipulate files on the server, you must take particular care to assure that your server is secure before enabling mod_dav.

Any location on the server where DAV is enabled should be protected by authentication. The use of HTTP Basic Authentication is not recommended. You should use at least HTTP Digest Authentication, which is provided by the mod_auth_digest module. Nearly all WebDAV clients support this authentication method. An alternative is Basic Authentication over an SSL enabled connection.

In order for mod_dav to manage files, it must be able to write to the directories and files under its control using the User and Group under which Apache is running. New files created will also be owned by this User and Group. For this reason, it is important to control access to this account. The DAV repository is considered private to Apache; modifying files outside of Apache (for example using FTP or filesystem-level tools) should not be allowed.

mod_dav may be subject to various kinds of denial-of-service attacks. The LimitXMLRequestBody directive can be used to limit the amount of memory consumed in parsing large DAV requests. The DavDepthInfinity directive can be used to prevent PROPFIND requests on a very large repository from consuming large amounts of memory. Another possible denial-of-service attack involves a client simply filling up all available disk space with many large files. There is no direct way to prevent this in Apache, so you should avoid giving DAV access to untrusted users.

Complex Configurations

One common request is to use mod_dav to manipulate dynamic files (PHP scripts, CGI scripts, etc). This is difficult because a GET request will always run the script, rather than downloading its contents. One way to avoid this is to map two different URLs to the content, one of which will run the script, and one of which will allow it to be downloaded and manipulated with DAV.

Alias /phparea /home/gstein/php_files Alias /php-source /home/gstein/php_files <Location /php-source> DAV On ForceType text/plain </Location>

With this setup, http://example.com/phparea can be used to access the output of the PHP scripts, and http://example.com/php-source can be used with a DAV client to manipulate them.

Dav Directive

Description:	Enable WebDAV HTTP methods
Syntax:	`Dav On\|Off\|provider-name`
Default:	`Dav Off`
Context:	directory
Status:	Extension
Module:	mod_dav

Use the Dav directive to enable the WebDAV HTTP methods for the given container:

<Location /foo> Dav On </Location>

The value On is actually an alias for the default provider filesystem which is served by the mod_dav_fs module. Note, that once you have DAV enabled for some location, it cannot be disabled for sublocations. For a complete configuration example have a look at the section above.

Do not enable WebDAV until you have secured your server. Otherwise everyone will be able to distribute files on your system.

DavDepthInfinity Directive

Description:	Allow PROPFIND, Depth: Infinity requests
Syntax:	`DavDepthInfinity on\|off`
Default:	`DavDepthInfinity off`
Context:	server config, virtual host, directory
Status:	Extension
Module:	mod_dav

Use the DavDepthInfinity directive to allow the processing of PROPFIND requests containing the header 'Depth: Infinity'. Because this type of request could constitute a denial-of-service attack, by default it is not allowed.

DavMinTimeout Directive

Description:	Minimum amount of time the server holds a lock on a DAV resource
Syntax:	`DavMinTimeout seconds`
Default:	`DavMinTimeout 0`
Context:	server config, virtual host, directory
Status:	Extension
Module:	mod_dav

When a client requests a DAV resource lock, it can also specify a time when the lock will be automatically removed by the server. This value is only a request, and the server can ignore it or inform the client of an arbitrary value.

Use the DavMinTimeout directive to specify, in seconds, the minimum lock timeout to return to a client. Microsoft Web Folders defaults to a timeout of 120 seconds; the DavMinTimeout can override this to a higher value (like 600 seconds) to reduce the chance of the client losing the lock due to network latency.

Example

<Location /MSWord> DavMinTimeout 600 </Location>