XML External Entity (XXE) Injection Affecting org.apache.tika:tika-parsers package, versions [1.6,1.13)
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27 May 2016
27 May 2016
Arthur Khashaev, Seulgi Kim, Mesut Timur, Microsoft Vulnerability Research
Affected versions of the package are vulnerable to XML External Entity (XXE) Injection. Apache Tika parses XML within numerous file formats. In some instances, the initialization of the XML parser or the choice of handlers did not protect against XML External Entity (XXE) vulnerabilities.
 Spreadsheets in OOXML files and XMP in PDF and other file formats.
XXE Injection is a type of attack against an application that parses XML input. XML is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. By default, many XML processors allow specification of an external entity, a URI that is dereferenced and evaluated during XML processing. When an XML document is being parsed, the parser can make a request and include the content at the specified URI inside of the XML document.
Attacks can include disclosing local files, which may contain sensitive data such as passwords or private user data, using file: schemes or relative paths in the system identifier.
For example, below is a sample XML document, containing an XML element- username.
<?xml version="1.0" encoding="ISO-8859-1"?> <username>John</username> </xml>
An external XML entity -
xxe, is defined using a system identifier and present within a DOCTYPE header. These entities can access local or remote content. For example the below code contains an external XML entity that would fetch the content of
/etc/passwd and display it to the user rendered by
<?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE foo [ <!ENTITY xxe SYSTEM "file:///etc/passwd" >]> <username>&xxe;</username> </xml>
Other XXE Injection attacks can access local resources that may not stop returning data, possibly impacting application availability and leading to Denial of Service.