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Security

The XPointer processor will evaluate XPath expressions contained in the pointer. This can lead to security issues, especially when deployed on a server that is accessible from internet. Even when running on your local machine, you should process only pointer expressions that you trust to be non-malicious.

The security risk

An XPath expression can be crafted to read an arbitrary file and send it to an arbitrary server on the internet.

Using unparsed-text(), also non-XML files like /etc/passwd and other system configurations can be read.

Unless you take counter measures, the XPath expression can be crafted in a way, so that no exception occurs. Thus, you will not even notice, that a file was stolen.

All files accessible with the privileges of the XPointer processors system process are exposed to this thread.

Counter measures

Server

When deployed on a web server, take the following counter measures:

  1. Allow access to documents via remote protocols like http(s) and ftp(s) only. Disallow access via the file protocol.

This can be achieved by setting restricting the protocols via the Saxon configuration file.

<configuration xmlns="http://saxon.sf.net/ns/configuration"
    edition="HE"
    label="Hardened configuration">

  <global
      allowedProtocols="http,https,ftp,ftps"
      unparsedTextURIResolver="net.sf.saxon.lib.StandardUnparsedTextResolver"
      uriResolver="net.sf.saxon.lib.StandardURIResolver"
	  />

  <!-- ... -->

</configuration>

Local machine

  1. Unless you fully trust the XPath expressions in the processed XPointers, consider setting allowedProtocols="file" in the Saxon config file. This is the default setting in saxon/saxon-config.xml.

  2. Also consider setting uriResolver="org.teic.teixptr.implementation.security.DenyingURIResolver" which serves an extra gatekeeper behind the closed door.

When you find more security risks

When you found a security issue, please do not post it into the issue tracker, but first report it via private mail to one of the developers or to scdh (at) uni-muenster (dot) de.