CVE-2020-35852 in Chatbot
Summary
by MITRE • 02/23/2021
Chatbox is affected by cross-site scripting (XSS). An attacker has to upload any XSS payload with SVG, XML file in Chatbox. There is no restriction on file upload in Chatbox which leads to stored XSS.
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Analysis
by VulDB Data Team • 03/04/2021
The vulnerability identified as CVE-2020-35852 affects the Chatbox application and represents a critical cross-site scripting flaw that enables persistent malicious code execution. This vulnerability stems from inadequate input validation and file upload restrictions within the application's file handling mechanisms. The security weakness allows attackers to bypass normal upload restrictions by submitting specially crafted SVG or XML files containing malicious JavaScript payloads. These files are stored within the application's file system and subsequently executed when other users access the chat interface, creating a stored XSS attack vector that can compromise user sessions and execute unauthorized commands on behalf of victims.
The technical implementation of this vulnerability leverages the inherent trust that web applications place in file extensions and content types during upload processes. When users upload SVG or XML files through the Chatbox interface, the application fails to perform adequate content validation or sanitization checks that would normally prevent malicious code from being stored and executed. This flaw aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities in web applications, and represents a classic case of stored XSS where malicious payloads are permanently stored on the server and executed when accessed by other users. The vulnerability is particularly dangerous because it requires no user interaction beyond the initial file upload, making it a persistent threat that can affect multiple users over time.
The operational impact of this vulnerability extends beyond simple data theft or session hijacking, as it provides attackers with the ability to execute arbitrary code within the context of other users' browsers. This capability allows threat actors to perform actions such as stealing cookies, redirecting users to malicious sites, defacing the chat interface, or even establishing persistent backdoors within the application environment. The stored nature of the XSS payload means that the vulnerability remains active until the malicious files are removed from the system, potentially affecting all users who interact with the chat functionality. The attack surface is particularly concerning given that chat applications typically handle sensitive communications and user data, making this vulnerability a prime target for espionage and data exfiltration campaigns.
Mitigation strategies for CVE-2020-35852 must address both the immediate security gap and implement comprehensive file handling controls. Organizations should implement strict file type validation and content sanitization mechanisms that prevent any executable code from being stored within the application's file system, regardless of file extension. This includes implementing MIME type checking, file content analysis, and the removal of dangerous file types from the upload whitelist. The solution should also incorporate proper input sanitization and output encoding techniques to prevent any stored content from being executed as JavaScript. Additionally, implementing principle of least privilege access controls and regular security audits of uploaded files can help detect and prevent unauthorized file uploads. This vulnerability demonstrates the importance of defense-in-depth strategies and aligns with ATT&CK technique T1566, which covers credential access through phishing and malicious file downloads, emphasizing that file upload vulnerabilities can serve as initial access vectors for broader compromise operations.