Dev Blog v1.0 - Stored XSS

Vulnerability

Dev blog v1.0, a Node.js (Express) and MongoDB blog application, contains a stored cross-site scripting (XSS) vulnerability due to an unrestricted file upload mechanism combined with poor filename entropy. The application does not validate uploaded file types, allowing an attacker to upload arbitrary files, including HTML files containing malicious JavaScript. Additionally, filenames are generated with insufficient randomness, making them predictable. This issue affects version 1.0 as described in the project repository [1] and the advisory [2].

Exploitation

An attacker can upload a malicious HTML file containing an XSS payload via the file upload functionality. Due to the low entropy of generated filenames, the attacker can guess or brute-force the filename of the uploaded file. The attacker then sends a crafted link to a potential victim, pointing to the uploaded file. When the victim accesses the link, the malicious HTML is rendered in their browser, executing the attacker's JavaScript in the context of the application [2].

Impact

Successful exploitation allows the attacker to execute arbitrary JavaScript in the victim's browser. This can lead to theft of session cookies, exfiltration of sensitive data, or performing actions on behalf of the victim within the Dev blog application. The impact is limited to the user's session and data accessible through the application [2].

Mitigation

As of the publication date, no official patch is available for this vulnerability [2]. Mitigations include restricting file uploads to only allowed file types (e.g., images), implementing strong random filenames (e.g., using UUIDs), and serving uploaded files with appropriate Content-Disposition headers to prevent direct HTML rendering. The application is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.