CVE-2026-27605: Depomo Chartbrew XSS Vulnerability

CVE-2026-27605 Overview

CVE-2026-27605 is a Cross-Site Scripting (XSS) vulnerability in Chartbrew, an open-source web application used for connecting to databases and APIs to create data visualizations. The vulnerability exists in the project logo upload functionality, which fails to properly validate file types or content before saving files to the uploads/ directory. This allows attackers to upload malicious HTML files containing JavaScript that executes in victims' browsers, potentially leading to account takeover through theft of authentication tokens stored in localStorage.

Critical Impact

Attackers can upload malicious HTML files as project logos, enabling stored XSS attacks that can steal authentication tokens and lead to complete account takeover of affected Chartbrew users.

Affected Products

• Depomo Chartbrew versions prior to 4.8.4

Discovery Timeline

• 2026-03-06 - CVE-2026-27605 published to NVD
• 2026-03-10 - Last updated in NVD database

Technical Details for CVE-2026-27605

Vulnerability Analysis

The vulnerability stems from insufficient input validation in Chartbrew's file upload functionality for project logos. The application accepts user-provided file extensions without verifying that the actual file content matches the expected file type. When a user uploads a file, the system stores it in the uploads/ directory and serves it statically to users, creating an opportunity for stored XSS attacks.

Since Chartbrew stores authentication tokens in the browser's localStorage (as evidenced by tokens being returned in API response bodies), a successful XSS attack can extract these credentials. An attacker with low-privilege access can upload a malicious HTML file disguised as a project logo, and when other users view the affected content, the embedded JavaScript executes in their browser context, enabling session hijacking and account takeover.

Root Cause

The root cause of this vulnerability is the lack of server-side file type validation in the project logo upload feature. The application trusts the file extension provided by the user without performing content-type verification or sanitization. This violates the security principle of never trusting user input, particularly for file uploads that will be served to other users.

Attack Vector

The attack vector is network-based and requires low privileges (an authenticated user account) along with user interaction (a victim must view the malicious content). An attacker uploads an HTML file containing malicious JavaScript as a project logo. The file is saved with its original extension and served statically. When another user accesses the uploaded file, the browser renders it as HTML and executes the embedded script, which can then exfiltrate authentication tokens from localStorage to an attacker-controlled server.

The attack is considered to have a changed scope because it affects resources beyond the vulnerable component—specifically, it can compromise other users' sessions and accounts.

Detection Methods for CVE-2026-27605

Indicators of Compromise

• Presence of .html, .htm, .svg, or other executable file types in the uploads/ directory
• Unusual file content in project logo files containing <script> tags or JavaScript event handlers
• Unexpected outbound network requests originating from user browsers after viewing project pages
• Authentication token reuse from different IP addresses or user agents

Detection Strategies

• Implement file upload monitoring to alert on non-image file types being saved to the uploads/ directory
• Deploy Content Security Policy (CSP) headers to detect and block inline script execution
• Monitor web server access logs for requests to files with suspicious extensions in the uploads path
• Review application logs for upload activity from accounts attempting multiple file types

Monitoring Recommendations

• Enable real-time alerting for file uploads with HTML, SVG, or executable extensions
• Monitor localStorage access patterns in browser telemetry for signs of token exfiltration
• Implement network-level monitoring for data exfiltration attempts to unknown external domains
• Track authentication anomalies such as session tokens being used from multiple geographic locations

How to Mitigate CVE-2026-27605

Immediate Actions Required

• Upgrade Chartbrew to version 4.8.4 or later immediately
• Audit the uploads/ directory for any existing HTML, SVG, or other potentially malicious files
• Implement Content Security Policy headers to mitigate the impact of any existing malicious uploads
• Review recent authentication logs for signs of unauthorized access or token theft

Patch Information

This vulnerability has been patched in Chartbrew version 4.8.4. The fix implements proper file type validation for uploaded project logos. Organizations should upgrade to this version or later to remediate the vulnerability. For more details, see the GitHub Security Advisory and release notes for v4.8.4.

Workarounds

• Configure web server rules to prevent serving HTML files from the uploads/ directory
• Implement a reverse proxy rule to force Content-Disposition: attachment for all files in the uploads path
• Add X-Content-Type-Options: nosniff header to prevent MIME-type sniffing
• Restrict file upload functionality to trusted administrator accounts until patching is complete

# Nginx configuration example to mitigate the vulnerability
location /uploads/ {
    # Force download instead of rendering files
    add_header Content-Disposition "attachment";
    # Prevent MIME-type sniffing
    add_header X-Content-Type-Options "nosniff";
    # Only allow specific image types
    location ~* \.(html|htm|svg|js)$ {
        deny all;
    }
}