CVE-2016-5661 in Civic
Summary
by MITRE
Accela Civic Platform Citizen Access portal relies on the client to restrict file types for uploads, which allows remote authenticated users to execute arbitrary code via modified _EventArgument and filename parameters.
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Analysis
by VulDB Data Team • 11/01/2024
The CVE-2016-5661 vulnerability affects the Accela Civic Platform Citizen Access portal, a web-based system designed to facilitate citizen interactions with government services. This platform enables users to submit various types of files including documents, images, and other digital content through its web interface. The vulnerability stems from a critical flaw in the file upload validation mechanism where the system delegates the responsibility of file type restriction to the client-side browser rather than implementing server-side validation controls. This architectural weakness creates a significant security gap that can be exploited by malicious actors with authenticated access to the portal.
The technical flaw manifests through the manipulation of HTTP parameters, specifically the _EventArgument and filename parameters that are transmitted during file upload operations. When a user attempts to upload a file through the portal, the system expects these parameters to contain legitimate values that correspond to valid file types and upload operations. However, authenticated attackers can modify these parameters to bypass client-side validation checks and submit malicious files with executable code. The vulnerability is particularly dangerous because it leverages the trust relationship between the client and server, where the server assumes that client-side validation has already been properly enforced. This flaw aligns with CWE-434 which describes "Unrestricted Upload of File with Dangerous Type" and represents a classic example of insecure file upload handling that can lead to arbitrary code execution.
The operational impact of this vulnerability is severe and multifaceted. Remote authenticated users who have legitimate access to the Citizen Access portal can exploit this weakness to upload malicious files that may contain malware, backdoors, or other harmful code. Once uploaded, these files can be executed on the server, potentially allowing attackers to gain full control over the affected system. The implications extend beyond simple code execution as attackers can use this vulnerability to establish persistent access, escalate privileges, and move laterally within the network infrastructure. This type of vulnerability can compromise sensitive government data, disrupt public services, and potentially lead to broader security breaches within the civic platform ecosystem. The attack surface is particularly concerning given that the portal serves as a public-facing interface where citizens interact with government services, making it a prime target for exploitation.
Mitigation strategies for CVE-2016-5661 must focus on implementing robust server-side validation controls and eliminating client-side dependency for security enforcement. Organizations should implement strict file type validation on the server side using whitelisting approaches that only permit specific, safe file extensions and MIME types. The system must validate file content rather than relying solely on file extensions or MIME types derived from client parameters. Additionally, uploaded files should be stored in a secure location separate from the web root directory, and proper access controls should be implemented to prevent direct execution of uploaded content. Implementing input validation for the _EventArgument and filename parameters specifically can prevent parameter manipulation attacks. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for suspicious upload activities. This vulnerability demonstrates the critical importance of defense in depth principles and the necessity of server-side validation as the ultimate authority for security decisions, aligning with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1078 for Valid Accounts which are commonly used in exploitation scenarios following initial access through file upload vulnerabilities.