XML External Entity (XXE) Injection Affecting org.apache.poi:poi-ooxml Open this link in a new tab package, versions [,4.1.0)
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13 Feb 2020
13 Feb 2020
Artem Smotrakov from SAP
How to fix?
org.apache.poi:poi-ooxml to version 4.1.0 or higher.
org.apache.poi:poi-ooxml is a Java API To Access Microsoft Format Files.
Affected versions of this package are vulnerable to XML External Entity (XXE) Injection. When using the tool
XSSFExportToXml to convert user-provided Microsoft Excel documents, a specially crafted document can allow an attacker to read files from the local filesystem or from internal network resources via XML External Entity (XXE) Processing.
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> <?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> <?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.