CVE-2018-17874 in ExpressionEngine
Summary
by MITRE
ExpressionEngine before 4.3.5 has reflected XSS.
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Analysis
by VulDB Data Team • 03/28/2020
ExpressionEngine versions prior to 4.3.5 contain a reflected cross-site scripting vulnerability that allows remote attackers to inject malicious scripts into web pages viewed by other users. This vulnerability occurs when the application fails to properly sanitize user input before reflecting it back in HTTP responses, creating an opportunity for attackers to execute arbitrary JavaScript code within the victim's browser context. The flaw specifically affects how the application handles certain parameters in HTTP requests, particularly those related to search functionality and user input fields that are not adequately validated or escaped.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding practices within the ExpressionEngine framework. When user-supplied data is directly incorporated into web page responses without proper sanitization, attackers can craft malicious payloads that exploit the reflected XSS mechanism. This typically involves embedding script tags or other malicious code within URL parameters or form fields that are then echoed back to the user's browser. The vulnerability is classified as reflected XSS because the malicious script is reflected off the web server rather than being stored on the server itself, making it particularly challenging to detect and prevent through traditional server-side security measures.
The operational impact of CVE-2018-17874 extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal sensitive user credentials, manipulate web page content, or redirect users to malicious websites. Attackers can leverage this vulnerability to compromise user sessions, particularly if the application handles authentication tokens or session identifiers in the reflected parameters. The vulnerability affects any user interaction with the affected ExpressionEngine installation, making it a significant threat to websites that rely on this content management system for their online presence. Organizations using vulnerable versions face potential data breaches, unauthorized access to user accounts, and reputational damage from successful exploitation attempts.
Mitigation strategies for this vulnerability include immediate upgrade to ExpressionEngine version 4.3.5 or later, which contains the necessary patches to address the reflected XSS flaw. Additionally, implementing proper input validation and output encoding mechanisms can provide defense-in-depth measures that reduce the risk of exploitation even if other security controls fail. Organizations should also consider deploying web application firewalls to detect and block malicious requests targeting known XSS patterns. The vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in software applications. From an ATT&CK framework perspective, this vulnerability maps to techniques involving command and control communications and credential access through web application exploitation, potentially enabling adversaries to establish persistent access to affected systems through compromised user sessions. Regular security assessments and input validation reviews should be conducted to prevent similar vulnerabilities from emerging in future application versions.