CVE-2025-32371: DNN (DotNetNuke) XSS Vulnerability

CVE-2025-32371 Overview

CVE-2025-32371 affects DNN (formerly DotNetNuke), an open-source web content management system (CMS) in the Microsoft ecosystem. An attacker can craft a URL to the DNN ImageHandler that renders arbitrary text supplied through a querystring parameter into the generated image. Because the response originates from the trusted DNN domain, users viewing the resulting image may believe the embedded content is legitimate. This weakness maps to [CWE-451] User Interface Misrepresentation of Critical Information. The issue is fixed in DNN Platform version 9.13.4.

Critical Impact
Attackers can produce trusted-domain images containing attacker-controlled text, enabling phishing, brand impersonation, and social engineering campaigns hosted on legitimate DNN sites.

Affected Products

DNN Platform (formerly DotNetNuke) versions prior to 9.13.4
dnnsoftware:dotnetnuke component (DnnImageHandler.cs)
DNN-based CMS deployments exposing the ImageHandler endpoint

Discovery Timeline

2025-04-09 - CVE-2025-32371 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-32371

Vulnerability Analysis

The DNN ImageHandler accepts a querystring parameter that controls text rendered onto the returned image. Input passed through the URL is drawn directly into the image content without adequate validation or restriction. Because the resulting image is served from the DNN site's own origin, a viewer that trusts the domain may accept the embedded text as authentic content from the site operator. Attackers can therefore compose URLs that produce images containing fake announcements, fraudulent instructions, or impersonated brand messages. The flaw is a UI misrepresentation issue rather than code execution, but it enables convincing phishing lures because the image URL, TLS certificate, and origin all reference the legitimate DNN host.

Root Cause

The DnnImageHandler implementation in DNN Platform/Library/Services/GeneratedImage/DnnImageHandler.cs renders text from a querystring parameter into the produced image without sufficient authorization or input restriction. The fix introduces DotNetNuke.Common.Utilities and adds validation around the text-rendering path, along with an installer update at Install/Config/09.13.04.config.

Attack Vector

Exploitation is remote and requires user interaction: a victim must load or be directed to the attacker-crafted URL. No authentication is required to request the handler. Attackers typically distribute the malicious URL through email, chat, or embedded links on third-party sites, taking advantage of the trusted DNN domain in the image source.

text

// Patch excerpt: DNN Platform/Library/Services/GeneratedImage/DnnImageHandler.cs
     using System.Web;
 
     using DotNetNuke.Common;
+    using DotNetNuke.Common.Utilities;
     using DotNetNuke.Entities.Portals;
     using DotNetNuke.Services.FileSystem;
     using DotNetNuke.Services.GeneratedImage.FilterTransform;

Source: DNN Platform commit 5def7cc

Detection Methods for CVE-2025-32371

Indicators of Compromise

Web server access logs showing requests to ImageHandler.ashx or DnnImageHandler with unusually long or text-heavy querystring parameters.
Outbound links or email campaigns referencing image URLs on legitimate DNN sites that contain attacker-controlled text parameters.
Repeated requests to the image handler from a small set of source IPs, generating images with variations of the same text content.

Detection Strategies

Inspect DNN IIS logs for GET requests to the image handler containing text-rendering parameters not used by legitimate site templates.
Correlate referrer headers on image handler requests: legitimate traffic originates from the DNN site itself, while abuse often comes from external referrers or none at all.
Deploy a Web Application Firewall (WAF) rule to alert on image handler URLs whose text parameter exceeds a defined length or contains keywords used in phishing lures.

Monitoring Recommendations

Track DNN version inventory across hosted portals and flag any instance below 9.13.4.
Alert on spikes in ImageHandler request volume, which may indicate mass generation of phishing images.
Monitor brand-abuse and threat intelligence feeds for image URLs pointing back to your DNN domains.

How to Mitigate CVE-2025-32371

Immediate Actions Required

Upgrade all DNN Platform installations to version 9.13.4 or later.
Review the GitHub Security Advisory GHSA-2rrc-g594-rhqw for maintainer guidance.
Audit recent access logs for suspicious use of the image handler and preserve evidence for any confirmed phishing incidents.

Patch Information

The fix is delivered in DNN Platform 9.13.4 via commit 5def7cc2e7931bb1041b21540bde99f96874a5a9, which adjusts DnnImageHandler.cs and adds installer configuration at Install/Config/09.13.04.config. Administrators should apply the upgrade using the standard DNN upgrade package and validate portal functionality post-deployment.

Workarounds

Restrict access to the ImageHandler endpoint at the WAF or reverse proxy layer, blocking requests that include text-rendering parameters.
Rewrite or strip untrusted querystring parameters targeting the image handler until the patch is applied.
Educate site users and downstream consumers that images from the affected site may contain attacker-supplied text until the upgrade is complete.

bash

# Example IIS URL Rewrite rule to block text parameters on the DNN image handler
<rule name="Block DNN ImageHandler text param" stopProcessing="true">
  <match url="(?i)ImageHandler\.ashx" />
  <conditions>
    <add input="{QUERY_STRING}" pattern="(?i)(text|Text)=" />
  </conditions>
  <action type="AbortRequest" />
</rule>