CVE-2016-4003 in Struts
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the URLDecoder function in JRE before 1.8, as used in Apache Struts 2.x before 2.3.28, when using a single byte page encoding, allows remote attackers to inject arbitrary web script or HTML via multi-byte characters in a url-encoded parameter.
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Analysis
by VulDB Data Team • 07/24/2022
The vulnerability identified as CVE-2016-4003 represents a critical cross-site scripting flaw that emerged from a fundamental inconsistency in how Java runtime environments handle URL decoding operations. This issue specifically affects the URLDecoder function within JRE versions prior to 1.8, creating a dangerous condition where single-byte page encoding can be exploited to bypass security controls. The vulnerability manifests when Apache Struts 2.x frameworks process url-encoded parameters, particularly when multi-byte characters are involved in the encoding process, creating a pathway for malicious actors to inject arbitrary web scripts or HTML content into web applications.
The technical flaw stems from an improper handling of character encoding during URL decoding operations within the Java runtime environment. When a single-byte page encoding is specified but multi-byte characters are present in url-encoded parameters, the URLDecoder function fails to properly validate or sanitize the input data. This creates a condition where attackers can craft malicious payloads using multi-byte character sequences that appear legitimate to the decoding process but contain embedded script code. The vulnerability operates at the intersection of character encoding standards and web application security protocols, where the mismatch between expected and actual encoding behavior allows for code injection attacks.
The operational impact of this vulnerability extends far beyond simple script injection, as it provides attackers with the capability to execute arbitrary code within the context of affected web applications. Attackers can leverage this weakness to steal session cookies, perform unauthorized actions on behalf of users, redirect traffic to malicious sites, or even escalate privileges within the application environment. The vulnerability is particularly dangerous because it operates silently in the background, making detection difficult for security monitoring systems that may not recognize the subtle encoding manipulation techniques used to exploit it. This type of vulnerability directly violates the principle of input validation and demonstrates how encoding inconsistencies can create fundamental security weaknesses in web application frameworks.
Organizations utilizing affected versions of Apache Struts 2.x should immediately implement comprehensive mitigations including updating to patched versions of both the JRE and Apache Struts frameworks. The recommended approach involves upgrading to JRE 1.8 or later versions and Apache Struts 2.3.28 or higher, which contain the necessary fixes to properly handle URL decoding operations. Additional protective measures include implementing strict input validation routines that sanitize all url-encoded parameters, deploying web application firewalls with XSS detection capabilities, and configuring proper character encoding specifications throughout the application stack. Security teams should also conduct thorough code reviews to identify any custom implementations that might be vulnerable to similar encoding-related issues, while monitoring for any attempts to exploit this specific vulnerability through log analysis and intrusion detection systems. This vulnerability aligns with CWE-79 Cross-site Scripting and represents a typical example of how encoding inconsistencies can be exploited to bypass security controls, making it a prime target for automated exploitation tools and advanced persistent threats.