CVE-2024-23304

Executive Summary

CVE-2024-23304 is a denial-of-service (DoS) vulnerability affecting Cybozu KUNAI for Android versions 3.0.20 and 3.0.21. A remote, unauthenticated attacker can trigger a DoS condition by performing certain unspecified operations. The vulnerability has a CVSS score of 0.0 (likely unassigned or placeholder), and the EPSS score is 0.0%, indicating no active exploitation in the wild. No public proof-of-concept (PoC) or exploit code is available. The vendor has not released a patch, and the vulnerability remains unpatched as of the latest data.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary Android application (Cybozu KUNAI) distributed through official app stores. No supply chain compromise has been identified.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned value. Based on the description (remote, unauthenticated DoS), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): None (N)
• Integrity (I): None (N)
• Availability (A): High (H)

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Estimated Base Score: 7.5 (High)

Threat Level: Medium (due to low EPSS and no public exploit, but unpatched status increases risk).

Deep Dive & Mechanics

The vulnerability resides in Cybozu KUNAI for Android, a business application. The exact mechanism is not publicly disclosed, but the description indicates that a remote unauthenticated attacker can cause a denial-of-service condition by performing certain operations. This suggests a resource exhaustion or crash vulnerability triggered by malformed input or excessive requests.

Potential Attack Vector:

• The attacker sends specially crafted network requests to the KUNAI application (likely via its network service or API).
• The application fails to handle these requests properly, leading to excessive resource consumption (CPU, memory, or threads) or a crash.
• The DoS condition renders the application unavailable to legitimate users.

Root Cause: Likely a lack of input validation or improper handling of edge cases in the application's network communication layer.

Vulnerable vs. Patched Code

No patch is available. The vulnerable versions are 3.0.20 and 3.0.21. Without a patched version, a code comparison is not possible. The vendor (Cybozu) has not released a fix.

Exploitation & Lab Setup

No public exploit code is available. The following is a theoretical lab setup for testing.

Red Team (Attack Simulation)

1. Environment Setup:

   • Install Cybozu KUNAI for Android version 3.0.20 or 3.0.21 on an Android emulator or device.
   • Ensure the application is running and accessible over the network.

2. Attack Execution:

   • Use a tool like curl, netcat, or custom Python script to send malformed requests to the application's network service.
   • Example (hypothetical):

     # Send a large payload to trigger resource exhaustion
     python3 -c "print('A'*1000000)" | nc <target_ip> <port>
     

   • Alternatively, send a high volume of requests:

     # Use Apache Bench or custom script for DoS
     ab -n 10000 -c 100 http://<target_ip>:<port>/
     

3. Verification:

   • Monitor the application's responsiveness. If it becomes unresponsive or crashes, the DoS is successful.

Blue Team (Defense & Detection)

1. Network Monitoring:

   • Monitor for unusual traffic patterns to the KUNAI application, such as high request rates or abnormally large payloads.
   • Use intrusion detection systems (IDS) to alert on potential DoS attempts.

2. Application Hardening:

   • If possible, restrict network access to the KUNAI application using firewalls or VPNs.
   • Implement rate limiting on the application server side.

3. Incident Response:

   • If a DoS attack is detected, isolate the affected device or network segment.
   • Restart the application or device to restore service.

Indicators of Compromise (IOCs)

• Network IOCs:

  • High volume of requests to the KUNAI application's IP address and port.
  • Unusually large payload sizes in network packets.
  • Repeated connection attempts from a single source IP.

• Host IOCs:

  • Application crash logs (e.g., KUNAI has stopped).
  • High CPU or memory usage by the com.cybozu.kunai process.
  • Application unresponsiveness or force close events.

• File IOCs:

  • Log files containing error messages related to network timeouts or resource exhaustion.

Detection Engineering

YARA Rule

rule CVE_2024_23304_KUNAI_DoS {
    meta:
        description = "Detects potential DoS indicators for CVE-2024-23304 on Cybozu KUNAI Android"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-23304"
    strings:
        $s1 = "KUNAI" ascii wide nocase
        $s2 = "OutOfMemoryError" ascii wide
        $s3 = "java.lang.OutOfMemoryError" ascii wide
        $s4 = "SocketTimeoutException" ascii wide
        $s5 = "Connection reset" ascii wide
    condition:
        any of ($s*) and filesize < 10MB
}

Sigma Rule

title: CVE-2024-23304 - Cybozu KUNAI DoS Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects network patterns indicative of a DoS attack against Cybozu KUNAI for Android
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        dest_port: 8080  # Example port, adjust as needed
        duration: < 1
        orig_bytes: '> 1000000'
    condition: selection
falsepositives:
    - Legitimate large file transfers
level: high

Suricata Rule

alert tcp any any -> any 8080 (msg:"CVE-2024-23304 - Cybozu KUNAI DoS Attempt"; flow:to_server; content:"|00|"; depth:1; byte_test:1,>,100,0; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Actions:

  • Disable or uninstall Cybozu KUNAI for Android versions 3.0.20 and 3.0.21 until a patch is available.
  • Restrict network access to the application using firewall rules or VPNs.
  • Monitor for any unusual network traffic to the application.

• Long-term Actions:

  • Contact Cybozu support for patch availability and apply it as soon as released.
  • Implement network-level DoS protection (e.g., rate limiting, traffic filtering).
  • Consider using alternative applications if the vulnerability is not patched in a timely manner.

• Workarounds:

  • If the application is critical, isolate it on a separate network segment with strict access controls.
  • Use application-layer firewalls to inspect and filter traffic to the KUNAI service.

Valters IT
DevSecOps & Cyber Threat Intelligence