XML External Entity (XXE) Injection Affecting org.apache.lucene:lucene-queryparser package, versions [5.5.0,5.5.5) [6.0.0,6.6.2) [7.0.0,7.1.0)
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5 Nov 2017
21 Sep 2017
Michael Stepankin, Olga Barinova
How to fix?
org.apache.lucene:lucene-queryparser to versions 5.5.5, 6.6.2, 7.1.0 or higher.
Affected versions of
org.apache.lucene:lucene-queryparser are vulnerable to XML External Entity (XXE) Injection.
Remote code execution occurs in Apache Solr before 7.1 with Apache Lucene before 7.1 by exploiting XXE in conjunction with use of a Config API add-listener command to reach the
RunExecutableListener class. Note that the XML external entity expansion vulnerability occurs in the XML Query Parser which is available, by default, for any query request with parameters
deftype=xmlparser and can be exploited to upload malicious data to the
/upload request handler or as Blind XXE using ftp wrapper in order to read arbitrary local files from the Solr server. Note also that the second vulnerability relates to remote code execution using the
RunExecutableListener available on all affected versions of Solr.
Note: Elasticsearch, although it uses Lucene, is NOT vulnerable to this.
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.