Telco Security

SIP Security Attacks & Vulnerabilities

Comprehensive guide to Session Initiation Protocol (SIP) security vulnerabilities, attack vectors, and exploitation techniques for VoIP and IMS systems. Learn about registration hijacking, DoS attacks, authentication bypass, and message tampering.

SIP Attack Vectors

SIP Registration Hijacking
High
Overwrites legitimate user registrations with attacker-controlled contact information.

Impact:

Call hijacking, eavesdropping, and impersonation

Detection Indicators:

  • •Multiple REGISTER messages with different Contact fields
  • •Registration changes from unusual IP addresses

Mitigation:

  • •Implement TLS for SIP signaling
  • •Use strong authentication mechanisms
  • •Apply rate limiting
SIP Denial of Service
High
Overwhelms SIP servers with malformed or excessive traffic to disrupt service.

Impact:

Service unavailability, call processing disruption

Detection Indicators:

  • •Abnormal SIP traffic volumes
  • •Malformed SIP messages
  • •Unusual method patterns

Mitigation:

  • •Implement SIP-aware firewall
  • •Configure request throttling
  • •Deploy IDS/IPS systems
SIP Message Tampering
High
Intercepts and modifies SIP messages to alter call behavior or extract information.

Impact:

Call redirection, eavesdropping, media manipulation

Detection Indicators:

  • •Unexpected changes in SIP message content
  • •Unusual call routing patterns

Mitigation:

  • •Implement mutual TLS (mTLS)
  • •Use S/MIME for message encryption
  • •Apply SIP identity mechanisms
SIP Authentication Attacks
High
Breaks or bypasses SIP authentication mechanisms for unauthorized access.

Impact:

Unauthorized service usage, toll fraud, impersonation

Detection Indicators:

  • •Failed authentication attempts
  • •Authentication from unusual sources
  • •Brute force patterns

Mitigation:

  • •Use strong digest authentication
  • •Implement account lockout
  • •Apply IP-based restrictions

SIP Security Testing Methodology

The methodology for testing SIP security combines network scanning, protocol analysis, authentication testing, and functional exploitation techniques.

1SIP Infrastructure Discovery
Identifying SIP components including proxies, registrars, gateways, and endpoints.

Techniques:

SIP OPTIONS scanningSIP server fingerprintingSIP extension discoveryDNS NAPTR/SRV record analysis

Tools:

SIPViciousSIP-ScanNmap SIP scripts
2Authentication Analysis
Testing the security of SIP authentication mechanisms.

Techniques:

Digest authentication crackingAuthentication bypass techniquesWeak credentials testingRegistration hijacking

Tools:

SIPcrackSIPVicious svcrackSIP Digest Leak Testing Tool
3Protocol Manipulation
Manipulating SIP messages to test for protocol-level vulnerabilities.

Techniques:

SIP message fuzzingMalformed packet handlingSIP header manipulationSDP content testing

Tools:

SIP Proxy FuzzerProtos SIP Test SuiteSIPp
4Service Exploitation
Testing specific SIP service vulnerabilities and attack scenarios.

Techniques:

Registration hijackingCall eavesdroppingSPIT (Spam over Internet Telephony)Toll fraud scenarios

Tools:

invitefloodRTP MixSoundSIPVicious

SIP Man-in-the-Middle Attack Flow

Step-by-Step Attack Sequence
Understanding how attackers intercept and manipulate SIP communications
1

Network Positioning

Attacker positions themselves in the network path between SIP endpoints or between endpoint and proxy.

Using ARP poisoning, DNS spoofing, or compromised network equipment to intercept traffic.

2

SIP Traffic Interception

Attacker captures SIP signaling traffic between the targeted parties.

Packet capture tools like Wireshark with VoIP analysis plugins can capture and decode SIP messages.

3

Call Setup Manipulation

During call establishment, attacker modifies the SDP (Session Description Protocol) information.

Changes media IP addresses and ports in SDP content to direct RTP media streams through attacker.

4

RTP Media Interception

Attacker receives the redirected media streams from both parties.

RTP packets flow through attacker, who can record or modify audio in real-time.

5

Media Relaying

Attacker forwards the media packets between parties to maintain the call connection.

Relays RTP packets between actual endpoints to avoid detection, optionally recording or modifying content.

6

Call Teardown Interception

Attacker continues monitoring until call completion, intercepting BYE messages.

May manipulate BYE requests or responses to extend the call duration if needed.

Related Attack Vectors

VoLTE Attacks
Voice over LTE security vulnerabilities and IMS exploitation
VoWiFi Attacks
WiFi calling security and ePDG exploitation techniques
Mobile Attacks
Comprehensive mobile network attack vectors and exploits

References & Standards