CVE-2014-3877 in fex
Summary
by MITRE
Incomplete blacklist vulnerability in Frams Fast File EXchange (F*EX, aka fex) before fex-20140530 allows remote attackers to conduct cross-site scripting (XSS) attacks via the addto parameter to fup.
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Analysis
by VulDB Data Team • 03/22/2022
The vulnerability identified as CVE-2014-3877 represents a critical security flaw in the Frams Fast File EXchange (FEX) application, specifically affecting versions prior to fex-20140530. This issue manifests as an incomplete blacklist vulnerability that directly enables cross-site scripting attacks through the addto parameter in the fup endpoint. The FEX application is designed for secure file transfer and management, making this vulnerability particularly concerning as it undermines the fundamental security assumptions of the system. The vulnerability exists within the input validation mechanism that is supposed to prevent malicious code execution by filtering user-supplied data.
The technical implementation of this vulnerability stems from inadequate sanitization of the addto parameter which is processed by the fup endpoint in the F*EX application. When a remote attacker submits malicious input through this parameter, the application fails to properly validate or sanitize the data before incorporating it into the web page response. This incomplete blacklist approach means that the system only blocks specific known malicious patterns rather than implementing comprehensive input validation or encoding mechanisms. The flaw allows attackers to inject arbitrary JavaScript code that executes in the context of other users' browsers, effectively bypassing the application's security controls. This vulnerability directly maps to CWE-79, which describes Cross-Site Scripting (XSS) vulnerabilities where insufficient input validation allows malicious scripts to be executed.
The operational impact of this vulnerability is substantial as it enables attackers to compromise user sessions and potentially access sensitive data within the FEX application. An attacker could exploit this vulnerability to steal session cookies, redirect users to malicious sites, or execute unauthorized actions on behalf of legitimate users. The attack surface is particularly broad since the vulnerability affects the file upload functionality, which is a core feature of FEX. Users who interact with the application could unknowingly be exposed to malicious code execution, potentially leading to complete system compromise if the application has elevated privileges or if users with administrative access are targeted. The vulnerability also aligns with ATT&CK technique T1566, which covers social engineering attacks through malicious file uploads, and T1203, which involves exploitation of vulnerabilities through web applications.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and output encoding mechanisms. The most effective approach involves replacing the incomplete blacklist with a comprehensive whitelist approach that only allows known safe characters and patterns. Additionally, implementing proper HTML entity encoding for all user-supplied data before rendering it in web pages would prevent script execution. The application should also implement Content Security Policy headers to provide additional protection against XSS attacks. Organizations should ensure immediate patching to fex-20140530 or later versions that address this specific vulnerability. Security monitoring should be enhanced to detect unusual patterns in the addto parameter usage, and regular security assessments should be conducted to identify similar input validation weaknesses in other components of the system. The remediation process should also include comprehensive testing of all user input handling mechanisms to prevent similar issues from arising in other parts of the application.