CVE-2016-3093 in Struts
Summary
by MITRE
Apache Struts 2.0.0 through 2.3.24.1 does not properly cache method references when used with OGNL before 3.0.12, which allows remote attackers to cause a denial of service (block access to a web site) via unspecified vectors.
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Analysis
by VulDB Data Team • 12/28/2018
Apache Struts 2 vulnerability CVE-2016-3093 represents a critical denial of service flaw that affects versions ranging from 2.0.0 through 2.3.24.1. This vulnerability stems from improper caching mechanisms within the framework's interaction with Object-Graph Navigation Language (OGNL) engine prior to version 3.0.12. The flaw manifests when the application processes method references within OGNL expressions, leading to a situation where cached method objects become corrupted or improperly managed during concurrent request processing. This caching issue creates a condition where the framework's internal method resolution system fails to properly handle method lookups, resulting in thread contention and resource exhaustion that ultimately blocks access to the affected web application.
The technical implementation of this vulnerability involves the Struts 2 framework's method resolution cache that stores references to methods accessed through OGNL expressions. When malicious input containing specially crafted OGNL expressions is processed, the framework's caching mechanism becomes overwhelmed with invalid or conflicting method references. The improper cache management causes the system to repeatedly attempt to resolve the same method references, leading to memory leaks and thread blocking conditions. This behavior creates a resource exhaustion scenario where legitimate requests cannot be processed due to the framework's inability to manage method references efficiently. The vulnerability operates at the application level and requires no authentication, making it particularly dangerous as attackers can exploit it without prior access credentials.
The operational impact of CVE-2016-3093 extends beyond simple service disruption to potentially compromise the entire web application availability. Attackers can leverage this vulnerability to perform sustained denial of service attacks that effectively shut down web services, causing significant business disruption and potential financial losses. The vulnerability's exploitation requires minimal technical expertise and can be automated, making it attractive to threat actors seeking to disable targeted web applications. Organizations running affected Struts versions face the risk of prolonged service outages that can last from minutes to hours, depending on the attack intensity and system resources. The vulnerability also creates indirect impacts including customer dissatisfaction, reputation damage, and potential regulatory compliance issues.
Security practitioners should prioritize immediate patching of affected Struts versions to address this vulnerability, with the recommended solution being an upgrade to Struts 2.3.24.2 or later, which includes the necessary OGNL caching fixes. Additionally, implementing input validation controls and limiting OGNL expression complexity can provide additional defense-in-depth measures. Network segmentation and monitoring systems should be configured to detect unusual patterns of method resolution requests that might indicate exploitation attempts. Organizations should also conduct comprehensive vulnerability assessments to identify all systems running affected Struts versions and establish incident response procedures for rapid remediation. This vulnerability aligns with CWE-400, which covers unrestricted resource consumption, and maps to ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the need for robust application-level security controls.
The broader implications of this vulnerability highlight the critical importance of proper caching mechanisms in enterprise web frameworks. This flaw demonstrates how seemingly minor implementation details in core framework components can create significant security risks. Organizations should implement comprehensive security testing procedures that include dynamic analysis of method resolution and caching behaviors, particularly for frameworks that heavily rely on expression languages. The vulnerability also underscores the necessity of maintaining current security patches and following secure coding practices that prevent resource management issues. Regular security assessments and vulnerability management programs become essential for preventing similar issues in other framework components that may exhibit similar caching or resource handling flaws.