CVE-2024-31404

Executive Summary

CVE-2024-31404 is an information disclosure vulnerability in Cybozu Garoon, a popular groupware platform in Japan. The flaw resides in the Scheduler module, where sensitive information is inserted into sent data, allowing an authenticated user to view data they should not have access to. This is a classic CWE-201: Insertion of Sensitive Information Into Sent Data issue. The vulnerability affects versions 5.5.0 through 6.0.0. No public exploit or patch details are currently available, but the risk is elevated for organizations using Garoon in multi-tenant or sensitive environments.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a proprietary web application vulnerability in Cybozu Garoon.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned by NVD)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): Low (authenticated user)
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): None
• Availability (A): None

Threat Level: Medium-High. While authentication is required, the ability to view other users' Scheduler data can lead to significant privacy breaches and lateral movement intelligence.

Deep Dive & Mechanics

The vulnerability is in the Scheduler module of Cybozu Garoon. When a user creates or views a schedule event, the application may inadvertently include sensitive information (such as attendee details, event notes, or internal references) in the data sent to the client. This data is then rendered in the browser, allowing an authenticated user to view information intended for other users or groups.

The root cause is likely a failure to properly filter or sanitize server-side data before sending it to the client. The Scheduler API endpoint may return all event details without checking the requesting user's permissions on each individual event.

Vulnerable vs. Patched Code

Since no patch is available, we can only hypothesize the fix. The vulnerable code likely looks like:

// Vulnerable: Returns all event data without permission check
app.get('/api/scheduler/events', (req, res) => {
    const events = db.getAllEvents();
    res.json(events);
});

The patched version would filter events based on the authenticated user's permissions:

// Patched: Filter events by user permissions
app.get('/api/scheduler/events', (req, res) => {
    const userId = req.user.id;
    const events = db.getEventsForUser(userId);
    res.json(events);
});

Exploitation & Lab Setup

Red Team

Prerequisites:

• A valid user account on a vulnerable Cybozu Garoon instance (v5.5.0 to v6.0.0).
• Network access to the Garoon web interface.

Exploitation Steps:

1. Log in to Garoon with a low-privileged user account.
2. Navigate to the Scheduler module.
3. Use browser developer tools to inspect the network requests when loading the scheduler.
4. Look for API endpoints like /api/scheduler/events or similar.
5. Modify the request parameters (e.g., userId, groupId) to request data for other users.
6. Observe the response containing sensitive schedule data.

Example curl command:

curl -X GET "https://target-garoon.example.com/api/scheduler/events?userId=admin" \
  -H "Cookie: GAROON_SESSION=valid_session_cookie"

Blue Team

Detection Steps:

1. Monitor for unusual API calls to the Scheduler module, especially with varying userId or groupId parameters.
2. Look for repeated requests from a single user to multiple different user IDs.
3. Check for anomalies in the size of API responses (e.g., a low-privileged user receiving large amounts of data).

Honeypot Strategy:

• Create a fake schedule event with a unique string (e.g., "HONEYPOT-EVENT-2024") and assign it to a high-value user.
• Monitor for any user accessing this event who should not have permission.

Indicators of Compromise (IOCs)

• Network: HTTP requests to /api/scheduler/events with multiple different userId parameters from the same source IP.
• Logs: Garoon access logs showing repeated 200 responses to the scheduler API from a single user for different user IDs.
• File: No specific file-based IOCs.

Detection Engineering

YARA Rule

rule CVE_2024_31404_Garoon_Scheduler_Disclosure {
    meta:
        description = "Detects potential exploitation of CVE-2024-31404 in Cybozu Garoon"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-31404"
    strings:
        $scheduler_api = "/api/scheduler/events" nocase
        $user_id_param = "userId=" nocase
        $group_id_param = "groupId=" nocase
    condition:
        $scheduler_api and ($user_id_param or $group_id_param)
}

Sigma Rule

title: CVE-2024-31404 - Cybozu Garoon Scheduler Information Disclosure
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential exploitation of CVE-2024-31404 by monitoring for unusual scheduler API requests.
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-uri-query|contains: "/api/scheduler/events"
    condition: selection
falsepositives:
    - Legitimate use of the scheduler API by administrators
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-31404 - Cybozu Garoon Scheduler Information Disclosure"; flow:to_server; content:"/api/scheduler/events"; http_uri; nocase; content:"userId="; http_uri; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: If a patch becomes available, upgrade to the latest version of Cybozu Garoon immediately.
2. Access Control: Review and tighten user permissions on the Scheduler module. Ensure users can only see events they are explicitly invited to.
3. Network Segmentation: Place Garoon behind a VPN or restrict access to trusted IP ranges.

Long-term Fixes:

• Implement server-side permission checks for all API endpoints.
• Conduct a security audit of all Garoon modules for similar issues.
• Enable detailed logging and monitoring for the Scheduler API.

Workaround:

• Disable the Scheduler module for non-essential users if possible.
• Use a Web Application Firewall (WAF) to block requests with suspicious userId or groupId parameters.

Valters IT
Securing Digital Frontiers