CVE-2017-7672 in Struts
Summary
by MITRE
If an application allows enter an URL in a form field and built-in URLValidator is used, it is possible to prepare a special URL which will be used to overload server process when performing validation of the URL. Solution is to upgrade to Apache Struts version 2.5.12.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/01/2021
The vulnerability identified as CVE-2017-7672 represents a critical denial of service flaw within Apache Struts web application framework that specifically affects applications utilizing the built-in URLValidator component. This vulnerability stems from insufficient input validation mechanisms that fail to properly handle maliciously crafted URL inputs, creating a scenario where legitimate server resources can be exhausted through carefully constructed payload sequences. The flaw operates at the application layer and demonstrates how seemingly benign validation processes can become attack vectors when proper resource management and input sanitization are lacking.
The technical implementation of this vulnerability exploits the URLValidator's processing logic by crafting URLs that trigger excessive computational overhead during validation routines. When an application accepts user input through form fields and subsequently processes this input through Apache Struts' URLValidator, attackers can construct specially formatted URLs that cause the validation process to consume disproportionate server resources. This occurs because the validator does not adequately limit the complexity or depth of URL structures it processes, allowing recursive or nested elements to accumulate and cause memory exhaustion or CPU overload conditions. The vulnerability aligns with CWE-400, which categorizes unchecked resource consumption as a fundamental weakness in software design and implementation practices.
From an operational perspective, this vulnerability presents a significant risk to web applications that rely on Apache Struts for URL validation and processing. Attackers can leverage this flaw to perform denial of service attacks against target servers, potentially causing service disruption for legitimate users while consuming server resources that could otherwise support legitimate application functions. The impact extends beyond simple service interruption as it can lead to system instability, performance degradation, and in severe cases complete application unavailability. The vulnerability demonstrates how input validation components, when improperly implemented, can become attack surfaces that enable resource exhaustion attacks against the underlying infrastructure.
Organizations utilizing affected Apache Struts versions should prioritize immediate remediation through upgrading to version 2.5.12 or later, which includes patched validation logic that properly handles resource consumption during URL processing. Additionally, implementing input validation controls at multiple layers of the application architecture can provide defense-in-depth strategies that mitigate the impact of similar vulnerabilities. Security practitioners should consider implementing rate limiting mechanisms and monitoring for unusual validation request patterns as part of their defensive measures. The vulnerability also underscores the importance of proper security testing and validation of third-party components, particularly those handling user input, as highlighted by ATT&CK technique T1499.004 for resource exhaustion attacks. Organizations should also implement comprehensive logging and monitoring to detect anomalous validation activities that may indicate exploitation attempts, while ensuring that all web applications undergo regular security assessments to identify and remediate similar implementation weaknesses.