CVE-2026-3070: Modern Image Gallery App XSS Vulnerability

CVE-2026-3070 Overview

A cross-site scripting (XSS) vulnerability has been identified in SourceCodester Modern Image Gallery App version 1.0. The vulnerability exists in the upload.php file, where improper handling of the filename argument allows attackers to inject malicious scripts. This flaw can be exploited remotely without authentication, enabling attackers to execute arbitrary JavaScript in the context of a victim's browser session.

Critical Impact

Attackers can inject malicious scripts through the filename parameter in the upload functionality, potentially leading to session hijacking, credential theft, or delivery of malicious content to end users.

Affected Products

• SourceCodester Modern Image Gallery App 1.0
• remyandrade modern_image_gallery_app 1.0

Discovery Timeline

• 2026-02-24 - CVE-2026-3070 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2026-3070

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting (XSS). The vulnerable component resides in the upload.php file of the Modern Image Gallery App. When a user uploads a file, the application fails to properly sanitize or encode the filename argument before reflecting it back in the response or storing it for later display.

The exploit has been publicly disclosed and documented. The network-based attack vector requires no prior authentication, though user interaction is necessary for successful exploitation. This typically manifests as a reflected or stored XSS scenario where the malicious payload executes when a victim views the affected page.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in the file upload functionality. The upload.php script accepts the filename parameter without properly sanitizing special characters such as angle brackets (<, >), quotation marks, or other HTML/JavaScript metacharacters. When this unsanitized input is subsequently rendered in the browser context, it enables script injection attacks.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can craft a malicious filename containing JavaScript code and submit it through the file upload functionality. The payload structure typically involves embedding script tags or event handlers within the filename value.

When the application processes the upload and reflects the filename back to users (either immediately or when browsing the gallery), the embedded script executes in the victim's browser. This can be used to steal session cookies, redirect users to phishing pages, perform actions on behalf of authenticated users, or deliver additional malicious payloads.

The vulnerability has been publicly disclosed through the GitHub CVE Issue Tracker, and additional technical details are available in the VulDB entry #347425.

Detection Methods for CVE-2026-3070

Indicators of Compromise

• Unusual characters or script tags present in uploaded filenames in application logs
• HTTP requests to upload.php containing encoded JavaScript payloads in the filename parameter
• Client-side error logs showing unexpected script execution from the gallery application domain
• User reports of unexpected browser behavior or redirections when viewing the image gallery

Detection Strategies

• Implement web application firewall (WAF) rules to detect XSS patterns in the filename parameter of requests to upload.php
• Monitor application logs for file upload requests containing HTML entities or JavaScript keywords such as <script>, onerror, onclick, or javascript:
• Deploy client-side Content Security Policy (CSP) violation reporting to identify attempted XSS attacks
• Review web server access logs for POST requests to upload.php with suspicious URL-encoded or double-encoded characters

Monitoring Recommendations

• Enable verbose logging on the web application to capture all file upload operations including full parameter values
• Configure intrusion detection systems (IDS) to alert on common XSS payload patterns targeting the application
• Implement real-time alerting for multiple failed upload attempts from single IP addresses that may indicate reconnaissance or exploitation attempts

How to Mitigate CVE-2026-3070

Immediate Actions Required

• Restrict access to the upload.php functionality to authenticated and authorized users only
• Implement input validation to reject filenames containing special characters or HTML/JavaScript content
• Apply output encoding to all user-controlled data before rendering in HTML context
• Consider temporarily disabling the file upload feature until a proper fix can be implemented

Patch Information

As of the last update on 2026-02-24, no official patch has been released by the vendor. Organizations using this software should monitor the SourceCodester website and the GitHub issue tracker for updates regarding security fixes.

SentinelOne Singularity provides protection against XSS-based attacks through behavioral analysis and can detect malicious script injection attempts. Customers should ensure their agents are updated to benefit from the latest threat intelligence.

Workarounds

• Implement server-side input validation to strip or reject filenames containing characters outside of a strict allowlist (alphanumeric, hyphens, underscores, and periods only)
• Apply HTML entity encoding to all filename outputs using language-appropriate functions such as htmlspecialchars() in PHP
• Deploy a Content Security Policy (CSP) header with strict directives to prevent inline script execution
• Use a WAF rule to block requests to upload.php containing potential XSS payloads in any parameter

# Example Apache mod_rewrite rule to block suspicious upload requests
# Add to .htaccess or Apache configuration
RewriteEngine On
RewriteCond %{QUERY_STRING} (<script|javascript:|onerror=|onclick=) [NC,OR]
RewriteCond %{REQUEST_BODY} (<script|javascript:|onerror=|onclick=) [NC]
RewriteRule ^upload\.php$ - [F,L]