CVE-2016-4433 in Struts
Summary
by MITRE
Apache Struts 2 2.3.20 through 2.3.28.1 allows remote attackers to bypass intended access restrictions and conduct redirection attacks via a crafted request.
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Analysis
by VulDB Data Team • 02/16/2019
Apache Struts 2 vulnerability CVE-2016-4433 represents a critical access control flaw that affects versions 2.3.20 through 2.3.28.1 of the popular web application framework. This vulnerability resides in the framework's parameter processing mechanism and enables remote attackers to bypass intended access restrictions by crafting specially designed requests that manipulate the action execution flow. The flaw specifically impacts the way Struts 2 handles parameter values during action execution, allowing malicious actors to redirect users to arbitrary URLs or execute unauthorized actions within the application context. The vulnerability is classified under CWE-285, which pertains to improper authorization, and aligns with ATT&CK technique T1071.004 for application layer protocol manipulation. The security implications extend beyond simple redirection attacks as attackers can potentially leverage this flaw to access restricted resources, perform unauthorized operations, or redirect users to malicious sites, making it a significant concern for organizations relying on Struts 2 for web application development.
The technical exploitation of CVE-2016-4433 occurs when the framework processes parameter values that contain special characters or sequences that alter the intended action execution path. Attackers can manipulate request parameters to bypass authentication checks or access control mechanisms that should normally prevent unauthorized access to specific actions or resources within the application. The vulnerability stems from insufficient validation of parameter values during the action execution lifecycle, where the framework fails to properly sanitize or validate input that could alter the expected behavior of the application's action chain. This flaw particularly affects applications that use the Struts 2 framework's parameter processing features, where the framework's default behavior allows parameter manipulation to influence action execution. The vulnerability's impact is amplified because it operates at the framework level rather than individual application code, meaning that any application built on affected Struts 2 versions could be compromised without requiring application-specific modifications or code changes.
Organizations utilizing affected Struts 2 versions face substantial operational risks from CVE-2016-4433, as the vulnerability enables attackers to conduct sophisticated redirection attacks that can lead to data breaches, unauthorized access to sensitive resources, and potential system compromise. The remote exploitation capability means that attackers can target vulnerable applications from outside the network perimeter, making the attack surface significantly larger than traditional network-based vulnerabilities. Security teams must consider that this vulnerability can be exploited to redirect users to phishing sites, execute unauthorized administrative functions, or access restricted application features that should only be available to authenticated users. The impact extends to business continuity and regulatory compliance, as organizations may face penalties for failing to protect sensitive data or maintain proper access controls. The vulnerability also demonstrates the importance of keeping enterprise frameworks updated, as the issue was resolved in Struts 2 version 2.3.29 and subsequent releases through enhanced parameter validation and access control mechanisms. Organizations should implement comprehensive monitoring to detect unusual redirection patterns or unauthorized access attempts that could indicate exploitation of this vulnerability.
Mitigation strategies for CVE-2016-4433 should prioritize immediate patching of affected Struts 2 versions to the latest secure releases, specifically upgrading to version 2.3.29 or later. Security teams should implement network-level controls including firewall rules that restrict access to Struts 2 endpoints and monitor for suspicious parameter patterns in web application logs. Application-level protections should include input validation for all parameters processed by Struts 2, particularly those that could influence action execution paths or redirect behavior. Organizations should also consider implementing web application firewalls that can detect and block malicious parameter sequences commonly used to exploit this vulnerability. The implementation of proper access control mechanisms within applications built on Struts 2 should include explicit authorization checks for all actions, even those that appear to be publicly accessible. Additionally, security monitoring should include detection of unusual redirection patterns or attempts to access restricted application resources, as these behaviors may indicate exploitation attempts. Regular security assessments and penetration testing should be conducted to verify that the implemented mitigations are effective and that no other vulnerabilities exist within the application stack. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date security frameworks and the need for comprehensive security testing throughout the application development lifecycle.