CVE-2016-6798: XML External Entity Reference in Apache Sling XSS Protection API
Summary
CVE-2016-6798: XML External Entity Reference in Apache Sling. Affects org.apache.sling:org.apache.sling.xss versions < 1.0.12. Fixed in 1.0.12. How to fix ↓
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Background
The Apache Sling XSS Protection API module is a part of the Apache Sling framework, which provides a set of tools and libraries for building web applications. The XSS Protection API module specifically focuses on preventing cross-site scripting (XSS) attacks by validating user input. However, a vulnerability in the module's XML parsing functionality allows for XML External Entity (XXE) attacks. This vulnerability affects all scripts that use the XSS.getValidXML() method, potentially enabling an attacker to read sensitive data, perform same-site-request-forgery (SSRF), port-scanning, or cause denial-of-service (DoS) attacks.
Vulnerability Detail
The vulnerability arises from the insecure SAX parser used by the XSS.getValidXML() method to validate input strings. This insecure parser allows for XXE attacks, where an attacker can include external entities in the XML input, leading to various malicious activities. These activities include reading sensitive data from the filesystem, performing SSRF attacks to access internal resources, scanning ports behind firewalls, or causing DoS by overwhelming the application. The severity of this vulnerability is rated as CRITICAL with a CVSS score of 9.8.
How To Fix
Minimum fixed version
1.0.12
This is the first release that contains the fix.
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Workaround
As a temporary workaround, developers can disable the use of the XSS.getValidXML() method or implement additional input validation and sanitization measures to prevent XXE attacks. However, it is strongly advised to apply the official patch by updating to the latest version of the module as soon as possible.
Conclusion
The Apache Sling XSS Protection API module is vulnerable to an XML External Entity (XXE) attack due to the use of an insecure SAX parser. This vulnerability can have severe consequences, including unauthorized data access, SSRF attacks, port scanning, and DoS. To fix this vulnerability, it is essential to update the module to version 1.0.12 or later. In the meantime, developers can apply temporary workarounds or additional input validation measures. For further support on vulnerability remediation, please contact DevNack.com.
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FAQ
Apache Sling is a web framework that provides a RESTful way to build web applications. It focuses on content-oriented applications and leverages Apache Jackrabbit for content storage.
An XML External Entity (XXE) attack is a type of attack where an attacker can exploit vulnerabilities in XML parsers to include external entities in the input, leading to various malicious activities.
This vulnerability can allow an attacker to read sensitive data on the filesystem, perform same-site-request-forgery (SSRF) attacks, scan ports behind firewalls, or cause denial-of-service (DoS) attacks on the application.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability. Vulert monitors and alerts in real-time for open-source vulnerabilities using just the pom.xml file.
At the time of this report, there are no known public exploits for this vulnerability. However, it is crucial to apply the recommended patch to mitigate the risk.
References
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