CVE-2013-2135 in Struts
Summary
by MITRE
Apache Struts 2 before 2.3.14.3 allows remote attackers to execute arbitrary OGNL code via a request with a crafted value that contains both "${}" and "%{}" sequences, which causes the OGNL code to be evaluated twice.
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Analysis
by VulDB Data Team • 01/03/2022
Apache Struts 2 vulnerability CVE-2013-2135 represents a critical remote code execution flaw that emerged in versions prior to 2.3.14.3. This vulnerability stems from improper handling of OGNL (Object-Graph Navigation Language) expressions within the framework's parameter processing mechanism. The flaw specifically manifests when a malicious request contains both "${}" and "%{}" sequences, creating a condition where OGNL expressions undergo double evaluation. This double evaluation occurs because the framework processes these sequences in a manner that allows the same code to be interpreted twice, effectively enabling an attacker to execute arbitrary code on the target system. The vulnerability operates at the application layer and can be exploited through HTTP requests without requiring authentication or additional privileges, making it particularly dangerous for web applications built on the Struts framework.
The technical exploitation of this vulnerability relies on the framework's parameter processing logic where OGNL expressions are evaluated twice in sequence. When a request parameter contains both "${}" and "%{}" constructs, the framework first processes the "${}" portion and then reprocesses the "%{}" portion, allowing the attacker to craft malicious payloads that execute unintended code. This double evaluation creates a code injection vector where attackers can leverage OGNL's powerful expression capabilities to execute system commands, access sensitive data, or manipulate the application's behavior. The vulnerability is classified under CWE-94 as "Improper Control of Generation of Code" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Python" and T1059.006 for "Command and Scripting Interpreter: PowerShell" when attackers leverage the executed code to perform further malicious activities. The flaw essentially allows attackers to bypass normal input validation mechanisms and execute arbitrary code with the privileges of the application server.
The operational impact of CVE-2013-2135 extends beyond simple code execution, as it provides attackers with a complete backdoor into affected systems. Successful exploitation can lead to full system compromise, data exfiltration, and persistent access to enterprise networks. Organizations running vulnerable Struts applications face significant risk since the attack surface includes any web application that accepts user input through parameters processed by the framework. The vulnerability's exploitation can result in unauthorized access to databases, file systems, and network resources, potentially enabling lateral movement within the organization. Security professionals must understand that this vulnerability can be weaponized through automated scanning tools and is often exploited in the wild as part of broader attack campaigns. The impact is particularly severe for applications handling sensitive data or serving as critical infrastructure components within enterprise environments.
Mitigation strategies for CVE-2013-2135 focus primarily on upgrading to Apache Struts 2.3.14.3 or later versions where the vulnerability has been addressed through proper handling of OGNL expression evaluation. Organizations should implement comprehensive patch management processes to ensure all affected systems receive updates promptly. Additional defensive measures include input validation and sanitization at multiple layers, implementing web application firewalls to detect and block suspicious parameter patterns, and monitoring for unusual request patterns that might indicate exploitation attempts. Security teams should also consider restricting network access to Struts applications, implementing least privilege principles for application servers, and conducting regular security assessments of web applications. The vulnerability's remediation requires careful testing of patches to ensure compatibility with existing applications, as upgrading may introduce breaking changes in parameter handling behavior. Organizations should also establish incident response procedures specifically for handling such vulnerabilities and maintain detailed logs of parameter processing to aid in forensic analysis should exploitation occur.