CVE-2025-59547: DNN CKEditor SSRF Vulnerability

CVE-2025-59547 Overview

CVE-2025-59547 affects DNN (formerly DotNetNuke), an open-source web content management system (CMS) built on the Microsoft stack. The CKEditor file upload endpoint fails to properly sanitize filenames containing Unicode characters. Attackers can craft upload requests that translate into paths capable of probing internal network endpoints. This weakness enables unauthenticated reconnaissance of resources inside the hosted site's private network. The issue is classified under [CWE-176] Improper Handling of Unicode Encoding. DNN released a fix in version 10.1.0.

Critical Impact
Unauthenticated attackers can leverage the CKEditor upload endpoint to probe internal network resources through crafted Unicode filenames, exposing information about hosts and services otherwise unreachable from the internet.

Affected Products

DNN Platform (DotNetNuke) versions prior to 10.1.0
Deployments exposing the CKEditor file upload endpoint
Self-hosted DNN CMS installations across Windows/IIS environments

Discovery Timeline

2025-09-23 - CVE-2025-59547 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-59547

Vulnerability Analysis

The vulnerability resides in the CKEditor file upload endpoint bundled with DNN. The endpoint accepts a filename parameter without adequately normalizing Unicode characters before path resolution. When an attacker submits a filename containing crafted Unicode sequences, the server transliterates or normalizes those characters into path components that reference network locations. The resulting path can point at UNC shares, loopback services, or internal hostnames rather than the intended upload directory. This turns a file upload primitive into a Server-Side Request Forgery (SSRF) style probe against the hosting environment.

The root category [CWE-176] describes exactly this class of failure: security decisions made on the pre-normalized form of input while file system or network resolution operates on the post-normalized form. Attackers exploit that gap to bypass allowlists and directory scoping checks.

Root Cause

The upload handler applies filename validation before Unicode normalization completes. Characters that appear benign in their raw form are later converted into path separators, drive prefixes, or UNC-style sequences by lower-level Windows or .NET APIs. The sanitizer never re-evaluates the normalized string, allowing traversal-like constructs to reach the resource resolution layer.

Attack Vector

The attack is remote and requires no authentication or user interaction. An adversary issues an HTTP request to the CKEditor upload endpoint with a filename embedding Unicode characters that decompose into path metacharacters. The server resolves the resulting path against internal resources and reveals whether hosts, shares, or services exist based on response timing and content. See the DNN GitHub Security Advisory GHSA-cgqj-mw4m-v7hp for vendor details.

No verified public exploit code is available. The vulnerability mechanism is described in prose per the vendor advisory.

Detection Methods for CVE-2025-59547

Indicators of Compromise

HTTP POST requests to CKEditor upload endpoints containing non-ASCII or Unicode escape sequences in the filename field
Upload requests where filenames decode into UNC paths, loopback references, or internal hostnames
Outbound SMB, HTTP, or DNS traffic originating from the DNN web application pool toward internal-only address ranges
Web server logs showing repeated upload attempts with varied Unicode payloads from a single source

Detection Strategies

Inspect IIS and application logs for CKEditor upload requests containing encoded characters such as %u, %c0, or full-width Unicode variants
Correlate upload requests with unexpected internal network connections from the DNN worker process
Deploy web application firewall (WAF) rules that reject upload filenames containing path separators after Unicode normalization

Monitoring Recommendations

Alert on egress traffic from web servers to RFC1918 addresses that do not match documented application dependencies
Track filename entropy and character-set distribution on upload endpoints to flag anomalous submissions
Enable verbose logging on the DNN CKEditor module and forward events to a centralized analytics platform for retrospective review

How to Mitigate CVE-2025-59547

Immediate Actions Required

Upgrade DNN Platform to version 10.1.0 or later, which contains the vendor fix
Restrict access to the CKEditor upload endpoint to authenticated editors and administrators through network or application-layer controls
Audit web server and application logs for prior exploitation attempts using Unicode-laden filenames

Patch Information

The vendor addressed the flaw in DNN Platform 10.1.0. Refer to the DNN Security Advisory GHSA-cgqj-mw4m-v7hp for release notes and the specific commits that harden filename sanitization against Unicode normalization bypass.

Workarounds

Block or restrict the CKEditor file upload route at the reverse proxy or WAF until the patch can be deployed
Enforce strict allowlists on upload filenames, rejecting any request containing non-ASCII characters
Segment the DNN web tier so it cannot reach internal management interfaces, file shares, or metadata services
Disable the CKEditor module for anonymous users where the site's editorial workflow permits

bash

# Example IIS URL Rewrite rule to block non-ASCII filenames on the CKEditor upload path
<rule name="Block-Unicode-CKEditor-Uploads" stopProcessing="true">
  <match url="Providers/HtmlEditorProviders/DNNConnect.CKE/.*Upload.*" />
  <conditions>
    <add input="{QUERY_STRING}" pattern="%[0-9A-Fa-f]{2}" />
  </conditions>
  <action type="CustomResponse" statusCode="400" statusReason="Bad Request" />
</rule>