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

CVE-2026-3070 Overview

CVE-2026-3070 is a cross-site scripting (XSS) vulnerability in SourceCodester Modern Image Gallery App 1.0, developed by remyandrade. The flaw resides in the upload.php file, where the filename argument is not properly sanitized before being reflected in application output. An unauthenticated remote attacker can manipulate the filename parameter to inject arbitrary script content. Successful exploitation requires user interaction, such as a victim viewing the affected page. The exploit details have been disclosed publicly, increasing the likelihood of opportunistic abuse against exposed deployments. This issue is tracked under CWE-79.

Critical Impact
Attackers can execute arbitrary JavaScript in the browser of any user interacting with crafted content delivered through upload.php, enabling session manipulation or content spoofing.

Affected Products

remyandrade Modern Image Gallery App 1.0
CPE: cpe:2.3:a:remyandrade:modern_image_gallery_app:1.0
Component: upload.php (filename parameter)

Discovery Timeline

2026-02-24 - CVE-2026-3070 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-3070

Vulnerability Analysis

The vulnerability is a reflected cross-site scripting flaw in the file upload handler of the Modern Image Gallery App. The application accepts user-supplied input through the filename argument processed by upload.php. The handler returns this value to the client without proper output encoding or input validation. As a result, an attacker can supply a filename value containing HTML or JavaScript syntax that the browser parses and executes within the application's origin. The attack vector is remote and requires no authentication, though the victim must interact with the malicious request or page. According to the public advisory, the exploit is already disclosed, so defenders should assume opportunistic scanning.

Root Cause

The root cause is missing input sanitization and output encoding in the upload.php handler. The filename parameter is incorporated into rendered HTML responses without applying context-aware escaping for HTML, attribute, or JavaScript contexts. This classifies as Improper Neutralization of Input During Web Page Generation under CWE-79.

Attack Vector

An attacker crafts a URL or upload request targeting upload.php and supplies a malicious payload in the filename parameter. The attacker delivers this URL to a target user through phishing, a malicious link, or an embedded reference. When the victim interacts with the request, the injected script executes in the victim's browser within the application's security context. This enables session token theft, defacement of the gallery interface, or pivoting to additional client-side attacks. See the public issue report and VulDB entry #347425 for technical specifics.

No verified proof-of-concept code is published in the realCodeExamples set. Consult the linked advisories for payload details.

Detection Methods for CVE-2026-3070

Indicators of Compromise

HTTP requests to upload.php containing script tags, javascript: URIs, or HTML event handlers in the filename parameter.
Unexpected outbound requests from user browsers immediately after visiting gallery pages, indicating script execution.
Web server access logs showing URL-encoded payloads such as %3Cscript%3E or onerror= patterns in query strings.

Detection Strategies

Deploy web application firewall (WAF) rules to flag XSS payload signatures targeting filename and similar upload parameters.
Monitor application logs for non-standard characters in filename fields, including angle brackets, quotes, and HTML entities.
Enable Content Security Policy (CSP) violation reporting to surface injection attempts that browsers block.

Monitoring Recommendations

Centralize web server and application logs and alert on anomalous upload.php request patterns.
Track session anomalies such as concurrent logins or unexpected privilege actions following gallery visits.
Review file upload audit trails for filenames containing scripting syntax even when uploads succeed.

How to Mitigate CVE-2026-3070

Immediate Actions Required

Restrict public access to the Modern Image Gallery App until a fix is applied, particularly any administrative or upload endpoints.
Apply server-side input validation that rejects filenames containing HTML metacharacters such as <, >, ", and '.
Configure a strict Content Security Policy that disables inline scripts and limits script sources to trusted origins.

Patch Information

No vendor patch is referenced in the available advisory data. Monitor the SourceCodester project page and the GitHub issue tracker for remediation updates. Until a vendor fix is released, apply compensating controls and consider removing the application from production exposure.

Workarounds

Sanitize and HTML-encode the filename parameter at the web server or reverse proxy layer using mod_security or equivalent WAF rules.
Enforce an allow-list for filename characters, permitting only alphanumeric values, dashes, and underscores.
Set the HttpOnly and Secure flags on session cookies to reduce the impact of successful script execution.

bash

# Example ModSecurity rule to block XSS payloads in the filename parameter
SecRule ARGS:filename "@rx (?i)(<script|javascript:|onerror=|onload=)" \
    "id:1002600,phase:2,deny,status:403,log,msg:'Possible XSS in upload.php filename parameter (CVE-2026-3070)'"