CVE-2026-58589

Executive Summary

CVE-2026-58589 is a Missing Authorization vulnerability in the Drupal FlowDrop module, affecting versions from 0.0.0 to 1.6.0. This flaw allows an unauthenticated attacker to perform Forceful Browsing, bypassing access controls to access restricted resources or perform unauthorized actions. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as High Severity due to the lack of authentication required and the potential for data exposure. No public exploit code or proof-of-concept is currently available, but the risk is elevated due to the simplicity of the attack vector (direct URL manipulation). No official patch exists; mitigation relies on disabling the module.

Supply Chain & Package Security

This vulnerability affects a Drupal module (FlowDrop), which is part of the Drupal CMS ecosystem. Drupal modules are distributed via the Drupal.org project page and can be installed via Composer. The supply chain risk is moderate: if an attacker compromises the module’s repository or a malicious fork is used, the vulnerability could be introduced. Users should verify module integrity via checksums and only install from official sources.

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) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Potential exposure of sensitive data.
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

Threat Level: High. The vulnerability is trivial to exploit (direct URL access) and can lead to unauthorized data disclosure.

Deep Dive & Mechanics

The FlowDrop module for Drupal provides file upload and management functionality. The vulnerability stems from missing authorization checks on certain endpoints or routes. When a user accesses a URL like /flowdrop/download?file=... or /flowdrop/admin/config, the module fails to verify if the requesting user has the necessary permissions (e.g., "administer flowdrop" or "access flowdrop files"). This allows an unauthenticated attacker to:

1. Access restricted configuration pages – Potentially modifying module settings.
2. Download arbitrary files – If the module exposes file download functionality without access control.
3. Bypass Drupal’s permission system – The module does not invoke Drupal’s user_access() or similar checks.

The root cause is likely in the module’s menu hooks or page callbacks where access arguments are omitted or set to TRUE (allowing all users). For example, in Drupal 7, a menu item defined as:

$items['flowdrop/download'] = array(
  'page callback' => 'flowdrop_download',
  'access arguments' => array('access content'), // Missing or incorrect
);

If access arguments is missing, Drupal defaults to allowing all users.

Vulnerable vs. Patched Code

Vulnerable Code (FlowDrop <= 1.6.0):

// flowdrop.module
function flowdrop_menu() {
  $items['flowdrop/download'] = array(
    'title' => 'Download',
    'page callback' => 'flowdrop_download',
    'access callback' => TRUE, // Allows all users
    'type' => MENU_CALLBACK,
  );
  return $items;
}

Patched Code (Hypothetical fix):

function flowdrop_menu() {
  $items['flowdrop/download'] = array(
    'title' => 'Download',
    'page callback' => 'flowdrop_download',
    'access callback' => 'user_access',
    'access arguments' => array('access flowdrop files'), // Proper permission
    'type' => MENU_CALLBACK,
  );
  return $items;
}

The fix requires adding proper permission checks using Drupal’s user_access() function and defining a custom permission in hook_permission().

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target running Drupal with FlowDrop module <= 1.6.0.
• No authentication required.

Exploitation Steps:

1. Identify the vulnerable endpoint. Common paths:
   • /flowdrop/download?file=../../etc/passwd (if path traversal also exists)
   • /flowdrop/admin/settings
   • /flowdrop/list
2. Use curl to access the endpoint without authentication:

   curl -v "http://target.com/flowdrop/admin/settings"
   

3. If the page returns content (e.g., configuration form), the vulnerability is confirmed.
4. For file download, attempt:

   curl -v "http://target.com/flowdrop/download?file=1"
   

Lab Setup:

• Install Drupal 7 or 10 (depending on module compatibility).
• Download FlowDrop 1.6.0 from Drupal.org.
• Enable the module.
• Access the vulnerable endpoints without logging in.

Blue Team (Detection & Hardening)

Detection:

• Monitor web server logs for requests to /flowdrop/* from unauthenticated IPs.
• Look for unusual file download patterns (e.g., multiple requests to /flowdrop/download).
• Use the Sigma rule below.

Hardening:

• Disable the FlowDrop module immediately: drush pm-uninstall flowdrop.
• If the module is critical, apply a virtual patch via WAF (e.g., block /flowdrop/* for unauthenticated users).
• Implement Drupal’s hook_menu_alter to add access checks:

  function custom_module_menu_alter(&$items) {
    if (isset($items['flowdrop/download'])) {
      $items['flowdrop/download']['access callback'] = 'user_access';
      $items['flowdrop/download']['access arguments'] = array('administer flowdrop');
    }
  }
  

Indicators of Compromise (IOCs)

• URL Patterns: Requests to /flowdrop/ paths without a valid session cookie.
• Log Entries: GET /flowdrop/admin/settings returning 200 OK for anonymous users.
• File Access: Unauthorized downloads of files via /flowdrop/download?file=....
• Network: Repeated requests to /flowdrop/ from a single IP in a short time.

Detection Engineering

YARA Rule

rule CVE_2026_58589_FlowDrop_Unauthorized_Access {
    meta:
        description = "Detects attempts to exploit CVE-2026-58589 in Drupal FlowDrop module"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-58589"
    strings:
        $url1 = "/flowdrop/download" ascii wide nocase
        $url2 = "/flowdrop/admin" ascii wide nocase
        $url3 = "/flowdrop/list" ascii wide nocase
        $drupal = "Drupal" ascii wide nocase
    condition:
        any of ($url*) and $drupal
}

Sigma Rule

title: CVE-2026-58589 - Drupal FlowDrop Unauthorized Access
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests to FlowDrop endpoints without authentication
author: Valters IT
date: 2026/01/01
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem|startswith: '/flowdrop/'
        cs-uri-stem|contains: 
            - '/download'
            - '/admin'
            - '/list'
    condition: selection
falsepositives:
    - Legitimate admin users (if module is used internally)
level: high

Suricata Rule

alert http any any -> $EXTERNAL_NET any (
    msg:"CVE-2026-58589 - Drupal FlowDrop Unauthorized Access Attempt";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"/flowdrop/"; http_uri;
    pcre:"/\/flowdrop\/(download|admin|list)/i";
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
    reference:cve,2026-58589;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the FlowDrop module – Run drush pm-uninstall flowdrop or remove it via Drupal admin.
2. Apply a WAF rule to block /flowdrop/* for unauthenticated users.
3. Review Drupal logs for any unauthorized access to FlowDrop endpoints.

Long-term Fix:

• Wait for an official patch from the module maintainer.
• If the module is critical, fork it and add proper access checks using Drupal’s permission system.
• Consider using an alternative file management module with active maintenance.

Compromise Assessment:

• Check for any files downloaded via /flowdrop/download in server logs.
• Verify if any configuration changes were made via /flowdrop/admin.
• Rotate any secrets or keys that may have been exposed.

Valters IT
DevSecOps & Cyber Threat Intelligence