XML External Entity (XXE) Injection Affecting org.apache.sling:org.apache.sling.xss package, versions [,1.0.12)


Severity

Recommended
0.0
critical
0
10

CVSS assessment made by Snyk's Security Team. Learn more

Threat Intelligence

EPSS
0.21% (60th percentile)

Do your applications use this vulnerable package?

In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.

Test your applications

Snyk Learn

Learn about XML External Entity (XXE) Injection vulnerabilities in an interactive lesson.

Start learning
  • Snyk IDSNYK-JAVA-ORGAPACHESLING-31466
  • published31 Aug 2017
  • disclosed9 Aug 2016
  • creditUnknown

Introduced: 9 Aug 2016

CVE-2016-6798  (opens in a new tab)
CWE-611  (opens in a new tab)

How to fix?

Upgrade org.apache.sling:org.apache.sling.xss to version 1.0.12 or higher.

Overview

org.apache.sling:org.apache.sling.xss is a framework for RESTful web-applications based on an extensible content tree.

Affected versions of the package are vulnerable to XML External Entity (XXE) Injection. In the XSS Protection API module before 1.0.12 in Apache Sling, the method XSS.getValidXML() uses an insecure SAX parser to validate the input string, which allows for XXE attacks in all scripts which use this method to validate user input, potentially allowing an attacker to read sensitive data on the filesystem, perform same-site-request-forgery (SSRF), port-scanning behind the firewall or DoS the application.

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.

References

CVSS Scores

version 3.1