CVE-2019-25400

Executive Summary

CVE-2019-25400 is a reflected cross-site scripting (XSS) vulnerability affecting IPFire 2.21 Core Update 127, specifically within the fwhosts.cgi script. An attacker can inject arbitrary JavaScript into multiple parameters of POST requests, which will execute in the context of an authenticated user's browser. This allows for session hijacking, credential theft, and other client-side attacks. The vulnerability has a CVSS score of 0.0 (likely unassigned or placeholder), but based on the vector, the actual severity is medium (CVSS 3.1 base score ~5.4). No official patch has been released, and no public exploit code is available, but the attack vector is well-documented.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby). It is a web application vulnerability in the IPFire firewall management interface.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Base Score: 5.4 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability is exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – The attacker does not need to be authenticated.
• User Interaction: Required (UI:R) – The victim must click a crafted link or submit a form.
• Scope: Changed (S:C) – The impact extends beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited information disclosure.
• Integrity Impact: Low (I:L) – Limited modification of data.
• Availability Impact: None (A:N) – No impact on system availability.

Threat Level: Medium. The vulnerability requires user interaction but can lead to session hijacking and credential theft in the context of the IPFire web interface.

Deep Dive & Mechanics

The vulnerability resides in the fwhosts.cgi script, which is part of the IPFire web interface for managing firewall hosts and services. The script fails to properly sanitize user-supplied input before reflecting it back in the HTTP response. An attacker can craft a POST request with malicious JavaScript payloads in any of the following parameters:

• HOSTNAME
• IP
• SUBNET
• NETREMARK
• HOSTREMARK
• newhost
• grp_name
• remark
• SRV_NAME
• SRV_PORT
• SRVGRP_NAME
• SRVGRP_REMARK
• updatesrvgrp

When an authenticated user submits the form or clicks a crafted link, the injected script executes in their browser. This allows the attacker to perform actions on behalf of the victim, such as modifying firewall rules, exfiltrating session cookies, or redirecting to malicious sites.

The root cause is the lack of output encoding or input validation. The script directly embeds user input into the HTML response without escaping special characters like <, >, ", ', and &.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

# In fwhosts.cgi (IPFire 2.21 Core Update 127)
my $hostname = param('HOSTNAME');
print "<input type='text' name='HOSTNAME' value='$hostname'>";

Patched Code (Conceptual):

# In a patched version
use CGI qw(:standard);
my $hostname = escapeHTML(param('HOSTNAME'));
print "<input type='text' name='HOSTNAME' value='$hostname'>";

The patched code uses escapeHTML() (or equivalent) to encode HTML special characters, preventing script injection.

Exploitation & Lab Setup

Red Team

Proof of Concept (PoC): Since no public exploit code is available, the following is a conceptual PoC.

1. Craft a malicious POST request:

   POST /cgi-bin/fwhosts.cgi HTTP/1.1
   Host: target-ipfire:444
   Content-Type: application/x-www-form-urlencoded
   Cookie: sid=valid_session_id
   
   HOSTNAME=<script>alert('XSS')</script>&IP=192.168.1.1&SUBNET=255.255.255.0&NETREMARK=test&HOSTREMARK=test&newhost=Add&grp_name=&remark=&SRV_NAME=&SRV_PORT=&SRVGRP_NAME=&SRVGRP_REMARK=&updatesrvgrp=
   

2. Deliver the attack:

   • Send a phishing email with a link to the crafted URL.
   • Use a social engineering technique to trick an authenticated admin into clicking the link.

3. Advanced payload:

   <script>
   fetch('/cgi-bin/fwhosts.cgi?action=delete&host=1').then(r => console.log('deleted'));
   </script>
   

Blue Team

Detection:

• Monitor for unusual POST requests to /cgi-bin/fwhosts.cgi containing HTML tags or JavaScript.
• Look for anomalous parameters with <script> or onerror attributes.
• Use WAF rules to block requests with XSS patterns.

Honeypot:

• Deploy a fake IPFire instance and log all POST requests to fwhosts.cgi for analysis.

Indicators of Compromise (IOCs)

• Network IOCs:
  • POST requests to /cgi-bin/fwhosts.cgi with parameters containing <script>, onerror, onload, or other event handlers.
  • Outbound connections from the IPFire web interface to unknown domains (exfiltration).
• Host IOCs:
  • Unusual entries in the IPFire web server logs (e.g., /var/log/httpd/access.log) with XSS payloads.
  • Modified firewall rules or host entries without admin knowledge.
• File IOCs:
  • No specific file-based IOCs.

Detection Engineering

YARA Rule

rule CVE_2019_25400_XSS_IPFire {
    meta:
        description = "Detects XSS payloads targeting IPFire fwhosts.cgi"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2019-25400"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $param1 = "HOSTNAME="
        $param2 = "IP="
        $param3 = "SUBNET="
        $param4 = "NETREMARK="
        $param5 = "HOSTREMARK="
        $param6 = "newhost="
        $param7 = "grp_name="
        $param8 = "remark="
        $param9 = "SRV_NAME="
        $param10 = "SRV_PORT="
        $param11 = "SRVGRP_NAME="
        $param12 = "SRVGRP_REMARK="
        $param13 = "updatesrvgrp="
    condition:
        any of ($xss*) and any of ($param*)
}

Sigma Rule

title: Reflected XSS in IPFire fwhosts.cgi
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects reflected XSS attempts against IPFire fwhosts.cgi
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/cgi-bin/fwhosts.cgi'
    xss_payloads:
        - cs-uri-query|contains: '<script'
        - cs-uri-query|contains: 'onerror='
        - cs-uri-query|contains: 'onload='
        - cs-uri-query|contains: 'alert('
        - cs-uri-query|contains: 'prompt('
        - cs-uri-query|contains: 'confirm('
    condition: selection and 1 of xss_payloads
falsepositives:
    - Legitimate use of HTML in hostnames (unlikely)
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (msg:"CVE-2019-25400 IPFire fwhosts.cgi Reflected XSS"; flow:to_server,established; content:"POST"; http_method; content:"/cgi-bin/fwhosts.cgi"; http_uri; pcre:"/(HOSTNAME|IP|SUBNET|NETREMARK|HOSTREMARK|newhost|grp_name|remark|SRV_NAME|SRV_PORT|SRVGRP_NAME|SRVGRP_REMARK|updatesrvgrp)=.*(<script|onerror|onload|alert|prompt|confirm)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade IPFire: If a newer version is available, upgrade immediately. As of this report, no official patch exists, so consider upgrading to the latest IPFire release (which may have fixed this issue in later updates).
2. Web Application Firewall (WAF): Deploy a WAF (e.g., ModSecurity) with rules to block XSS payloads in POST parameters.
3. Input Validation: Implement server-side input validation and output encoding for all parameters in fwhosts.cgi.
4. Content Security Policy (CSP): Add a strict CSP header to the IPFire web interface to mitigate XSS impact.
5. User Education: Train administrators to avoid clicking suspicious links and to verify the authenticity of requests.

Long-Term Fix:

• The vendor (IPFire) should release a security update that properly sanitizes all user inputs in fwhosts.cgi and other CGI scripts.

Valters IT