XML External Entity (XXE) Injection Affecting org.simpleframework:simple-xml package, versions [0,]


0.0
critical

Snyk CVSS

    Attack Complexity Low
    Confidentiality High
    Availability High

    Threat Intelligence

    EPSS 0.39% (73rd percentile)
Expand this section
NVD
9.1 critical

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  • Snyk ID SNYK-JAVA-ORGSIMPLEFRAMEWORK-31528
  • published 4 Oct 2017
  • disclosed 29 Sep 2017
  • credit LGTM Security Team, Man Yue Mo

How to fix?

There is no fixed version for org.simpleframework:simple-xml.

Overview

org.simpleframework:simple-xml is a RESTful Web API framework for Java.

Affected versions of the package are vulnerable to XML External Entity (XXE) Injection.

The XML External Entity (XXE) vulnerabilities abuse the XML specification to force an XML parser to either fetch sensitive data from the system, or carry out denial of services (DoS) or server-side request forgery (SSRF) attacks. The main problem is that the XML standard allows an XML document to define entities, which are like variables that can refer to resources outside of the XML document. Let's consider the following XML document:

<?xml version="1.0" encoding="ISO-8859-1"?>
 <!DOCTYPE foo [
  <!ELEMENT foo ANY >
  <!ENTITY abc SYSTEM "file:///etc/passwd" >]>
<foo>&abc;</foo>

This document defines an external entity named abc, that refers to the content of the file /etc/passwd. When the XML document is parsed, the entity &abc; will be replaced by the content of /etc/passwd. Now if an application is parsing XML data from an untrusted source, then by defining an external entity that points to a sensitive file, the attacker will be able to force the application to include sensitive data in the parsed XML document. If the attacker can then retrieve the content of the parsed document, they will be able to view the content of /etc/passwd.

  • LGTM Blog

Details

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 username.

<?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.