How SIP Engineering Works (VoIP Attacks)

[Man]

SIP engineering (or VoIP attacks) are methods of exploiting vulnerabilities in the Session Initiation Protocol (SIP), which governs the establishment, maintenance, and termination of voice and video calls over the Internet (VoIP). These attacks allow attackers to eavesdrop on conversations, intercept data, block communications, or make calls on behalf of the victim. However, it is important to emphasize that any use of these methods for illegal purposes is a criminal offense. The technical aspects of SIP engineering are described below for educational purposes.

1. What is SIP?​

SIP is a signaling protocol used to establish and manage communication sessions in VoIP networks. It operates on a client-server model and uses text messages (similar to HTTP) to:

• Registration of devices on the network.
• Establishing and ending calls.
• Transferring information about session parameters (e.g. audio/video codecs).

Example of SIP request:

INVITE sip:user@example.com SIP/2.0
Via: SIP/2.0/UDP 192.168.1.100:5060
From: <sip:caller@example.com>
To: <sip:callee@example.com>
Call-ID: 1234567890@example.com
CSeq: 1 INVITE
Content-Type: application/sdp
Content-Length: 142

v=0
o=caller 2890844526 2890844526 IN IP4 192.168.1.100
s=-
c=IN IP4 192.168.1.100
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000

2. How do SIP attacks work?​

A. SIP Session Interception (Man-in-the-Middle, MITM)​

• Purpose: Wiretapping calls or intercepting data.
• How it works:
  1. The attacker intercepts SIP requests (INVITE, REGISTER) by sniffing the network (for example, using Wireshark).
  2. Gets information about session parameters (IP addresses, ports, codecs).
  3. Intercepts RTP traffic (real audio/video stream) and plays it.

B. SIP Request Forgery (Spoofing)​

• Purpose: Making calls on behalf of the victim or manipulating sessions.
• How it works:
  1. The attacker modifies SIP request headers (e.g. From, Call-ID fields) to impersonate a legitimate user.
  2. Sends a fake INVITE request to start a call or a REFER request to redirect a call.
  3. The victim receives a call that appears to be from a trusted person, but is actually the attacker.

C. Registration Attacks (SIP Registration Hijacking)​

• Purpose: To intercept a user's account to control their calls.
• How it works:
  1. The attacker sends a REGISTER request with fake credentials (e.g. intercepted login/password).
  2. The SIP server accepts the request and associates the attacker's device with the victim's account.
  3. All incoming and outgoing calls from the victim are directed to the attacker's device.

D. Denial-of-Service (DoS) attacks​

• Purpose: Blocking communication or overloading the SIP server.
• How it works:
  1. The attacker sends a lot of fake SIP requests (such as INVITE or REGISTER) to exhaust the server's resources.
  2. The server becomes unavailable to legitimate users.

E. SIP Phishing​

• Purpose: To extract confidential data through fake calls.
• How it works:
  1. The attacker calls the victim, posing as a bank or support service employee.
  2. Uses fake Caller ID to make the number appear legitimate.
  3. Convinces the victim to provide passwords, 2FA codes, or transfer money.

3. SIP attack tools​

These tools are used by both attackers and security professionals to test vulnerabilities:

A. SIPVicious​

• Description: A set of tools for scanning and testing SIP servers.
• Possibilities:
  • svwar: Search for active SIP devices.
  • svcrack: Brute force credential selection.
  • sprecon: Intercept RTP traffic.
• Website: sipcrack.org

B. VoIPong​

• Description: A tool for analyzing and manipulating VoIP traffic.
• Possibilities:
  • Detecting RTP streams.
  • Play audio recordings in real time.

C. Wireshark​

• Description: Network traffic analyzer supporting SIP and RTP decoding.
• Possibilities:
  • Interception of SIP requests and responses.
  • Recovering audio recordings from RTP packets.
• Website: wireshark.org

D. Talk​

• Description: An open SIP platform that can be used by attackers to create fake servers.
• Possibilities:
  • Disguise as a legitimate SIP server.
  • Call interception and redirection.

4. Attack example: Call interception​

1. Network Scanning: The attacker uses svwar to search for active SIP devices in a range of IP addresses.
2. Session Interception: Using Wireshark, it captures the SIP INVITE request and extracts the RTP parameters (IP addresses and ports).
3. Playing audio: Using tools like rtpplay, the attacker plays the audio stream and listens to the conversation.

5. Why is SIP vulnerable?​

1. Lack of encryption: Many SIP systems do not use TLS or SRTP, leaving traffic open to eavesdropping.
2. Weak Authentication: SIP account passwords are often stored in cleartext or use simple hashing methods (e.g. MD5).
3. Header Trust: SIP requests are not checked for authenticity, allowing From and Call-ID to be spoofed.
4. Distributed architecture: SIP networks often include multiple entry points (e.g. PBXs, cloud services), making security more difficult.

6. How to protect yourself from SIP attacks?​

A. Traffic encryption​

• Use TLS to secure SIP signaling.
• Enable SRTP to encrypt RTP audio/video streams.

B. Strong Authentication​

• Set complex passwords for SIP accounts.
• Enable two-factor authentication (2FA) if supported.

C. Firewall Configuration​

• Configure your firewall to block suspicious traffic (e.g. mass REGISTER requests).
• Use SIP ALG (Application Layer Gateway) to filter SIP packets.

D. Updating systems​

• Regularly update SIP servers and client applications to eliminate vulnerabilities.
• Disable unnecessary features (eg anonymous calls).

E. Activity Monitoring​

• Use intrusion detection systems (IDS/IPS) such as Snort or Suricata to analyze SIP traffic.
• Set up alerts for suspicious activity (such as multiple login attempts).

F. Spoofing protection​

• Enable STIR/SHAKEN - Call authentication standards to prevent Caller ID spoofing.

7. Legal consequences​

SIP attacks violate the laws of many countries:

• USA: Computer Fraud and Abuse Act (up to 10 years in prison for wiretapping).
• Russia: Article 138 of the Criminal Code of the Russian Federation (unauthorized access to computer information).
• EU: GDPR (unlawful collection of personal data, fines up to €20 million).

8. Educational resources​

If you want to learn VoIP security legally:

• Books: "Hacking Exposed VoIP" (John Herlich), "VoIP Security" (Peter Laptev).
• Platforms: TryHackMe (VoIP security courses), OWASP.
• Certifications:
  • Certified Ethical Hacker (CEH) - network vulnerability analysis.
  • Cisco CCNP Security - Telecommunication Network Security.

Summary​

SIP engineering is a powerful tool that can be used for both defense and attack. Never try to use these techniques in real life - it is illegal and dangerous. Instead, focus on learning modern defense techniques and ethical hacking. If you are interested in practical examples or code for learning - let me know!

 

[Jollier]

SIP Engineering (VoIP Attacks): How Internet Telephony Is Hacked​

SIP (Session Initiation Protocol) is a standard protocol for establishing VoIP calls (Zoom, Skype, corporate PBX). Due to vulnerabilities in its implementation, attackers can:
✔ Eavesdrop on calls
✔ Make fraudulent calls at someone else's expense
✔ Disable telephony (DDoS)
✔ Steal credentials

How do SIP attacks work?​

1. Scanning and reconnaissance​

Attackers search for vulnerable VoIP servers using scanners (SIPVicious, Metasploit):

• Open ports 5060 (SIP), 5061 (SIP TLS)
• Weak or standard logins (admin:admin, user:1234)
• Outdated software (Asterisk, FreePBX with known bugs)

2. Basic attack methods​

SIP flood (DDoS on VoIP)​

• How it works: Sending thousands of SIP requests (INVITE, REGISTER) to overload the server.
• Result: The service "crashes", calls become impossible.

SIP spoofing (Caller ID substitution)​

• How it works: Substitution of the caller's number (for example, disguising it as a bank).
• Result: The victim trusts the fake call (vishing).

Brute-Force and Account Enumeration​

• How it works: Automated selection of passwords for SIP accounts.
• Result: Access to paid calls at someone else's expense.

Man-in-the-Middle (RTP traffic interception)​

• How it works: If there is no encryption (SRTP), voice packets can be intercepted.
• Result: Wiretapping.

Toll Fraud (International Fraudulent Calls)​

• How it works: Hacked VoIP account → calls to premium numbers ($10/min).
• Result: The victim receives a bill for thousands of dollars.

Real examples of attacks​

• 2021: Hackers hacked corporate IP-PBX, made calls worth $300K.
• 2023: Attack on Call Centers via Vulnerabilities in Asterisk (CVE-2023-26486).
• Common cases: Fraudsters call on behalf of banks with a spoofed number.

How to protect yourself?​

For business (VoIP servers)​

1. Use complex passwords + two-factor authentication.
2. Limit international calls (if not needed).
3. Enable encryption (SRTP, TLS for SIP).
4. Update software (Asterisk, FreePBX, Cisco CUCM).
5. Configure Fail2Ban to block brute-force.

For users​

1. Do not use SIP telephony with public servers (unless trusted).
2. Check suspicious calls (even from "familiar" numbers).
3. Disable SIP clients when not needed.

Legality​

• Hacking VoIP systems is a criminal offense (CFAA in the USA).
• But scammers often operate from countries where they are difficult to catch.

Conclusion: SIP engineering is a serious threat to businesses and private users. Protection requires setting up VoIP infrastructure security and being careful when making calls.

 

[Professor]

What is SIP Engineering and VoIP Attacks?​

SIP engineering is a type of attack on IP telephony systems that use the Session Initiation Protocol (SIP). SIP is the primary protocol used to establish, manage, and terminate VoIP calls. Vulnerabilities in SIP can be exploited by attackers to intercept data, compromise accounts, spoof calls, or even cause a denial of service (DoS).

How do SIP attacks work?​

1. Interception of authentication data:
   • SIP uses an authentication process based on HTTP Digest Authentication. An attacker can intercept SIP requests (e.g. REGISTER, INVITE) and extract the Authorization string containing data such as username, realm, nonce, and response. This data can be used to guess the client's password.
2. Server substitution (Man-in-the-Middle):
   • An attacker can pretend to be a SIP server and send a re-authentication request to the client. The client, unaware of the attack, sends its credentials, which the attacker intercepts and uses to register on the server on behalf of the victim.
3. Attacks on SIP Ports:
   • If SIP ports (usually 5060 or 5061) are open on the Internet, attackers can send malicious SIP requests directly to IP phones or servers. This allows them to initiate calls, intercept data, or even overload the system.
4. Denial of Service (DoS) attacks:
   • Attackers can send a large number of SIP requests (such as INVITE or REGISTER) to overload a server or phone system, resulting in a denial of service for legitimate users.
5. Fraud calls:
   • Once an attacker gains access to a SIP account, they can use it to make calls to premium numbers, resulting in financial losses for the account owner.

Examples of attacks​

• Call Interception: An attacker redirects SIP requests to listen in on or record calls.
• Account Compromise: Using weak passwords or intercepted data, an attacker gains access to a SIP account and uses it to make calls.
• Attacks on open SIP ports: IP phones or servers accessible via the Internet become targets for automated attacks aimed at guessing passwords or sending malicious requests.

How to protect yourself from SIP attacks?​

1. Use complex passwords:
   • Make sure your SIP accounts are protected with strong passwords to make them difficult to guess.
2. Encrypt SIP traffic:
   • Use encryption protocols such as TLS for SIP and SRTP for voice traffic to prevent data interception.
3. Restrict access to SIP ports:
   • Close SIP ports to external access or configure a firewall to limit the IP addresses that can connect to the server.
4. Use SIP proxy:
   • SIP proxy servers can filter requests and prevent direct communication between clients, reducing the risk of attacks.
5. Enable SIP firewalls:
   • Dedicated VoIP firewalls can detect and block suspicious SIP requests.
6. Monitoring and logging:
   • Regularly check your SIP server logs for suspicious activity, such as frequent registration attempts or abnormal calls.

Conclusion​

SIP engineering and VoIP attacks pose a serious threat to IP telephony systems, especially if they are improperly configured or unprotected. Using modern security methods such as encryption, complex passwords, and firewalls can significantly reduce the risk of attacks and ensure the security of your VoIP system.