8 min read

Voice over IP (VoIP) is pushing business communications to a new level of efficiency and productivity. VoIP-based systems are facing security risks on a daily basis. Although a lot of companies are focusing on the VoIP quality of service, they ignore the security aspects of the VoIP infrastructure, which makes them vulnerable to dangerous attacks.

This tutorial is an extract taken from the book Advanced Infrastructure Penetration Testing written by Chiheb Chebbi. In this book, you will explore exploitation abilities such as offensive PowerShell tools and techniques, CI servers, database exploitation, Active Directory delegation, and much more. In today’s post, you will learn how to penetrate the VoIP infrastructure.

Like any other penetration testing, to exploit the VoIP infrastructure, we need to follow a strategic operation based on a number of steps.

Before attacking any infrastructure, we’ve learned that we need to perform footprinting, scanning, and enumeration before exploiting it, and that is exactly what we are going to do with VoIP. To perform VoIP information gathering, we need to collect as much useful information as possible about the target. As a start, you can do a simple search online. For example, job announcements could be a valuable source of information. For example, the following job description gives the attacker an idea about the VoIP:

Later, an attacker could search for vulnerabilities out there to try exploiting that particular system. Searching for phone numbers could also be a smart move, to have an idea of the target based on its voicemail, because each vendor has a default one. If the administrator has not changed it, listening to the voicemail can let you know about your target. If you want to have a look at some of the default voicemails, check http://www.hackingvoip.com/voicemail.html. It is a great resource for learning a great deal about hacking VoIP.

Google hacking is an amazing technique for searching for information and online portals. We discussed Google hacking using Dorks. The following demonstration is the output of this Google Dork—in  URL: Network Configuration Cisco:

You can find connected VoIP devices using the Shodan.io search engine:

VoIP devices are generally connected to the internet. Thus, they can be reached by an outsider. They can be exposed via their web interfaces; that is why, sometimes leaving installation files exposed could be dangerous, because using a search engine can lead to indexing the portal. The following screenshot is taken from an online Asterisk management portal:

And this screenshot is taken from a configuration page of an exposed website, using a simple search engine query:

After collecting juicy information about the target, from an attacker perspective, we usually should perform scanning. Using scanning techniques is necessary during this phase. Carrying out Host Discovery and Nmap scanning is a good way of scanning the infrastructure to search for VoIP devices.

Scanning can lead us to discover VoIP services. For example, we saw the -sV option in Nmap to check services. In VoIP, if port 2000 is open, it is a Cisco CallManager because the SCCP protocol uses that port as default, or if there is a UDP 5060 port, it is SIP.

The -O Nmap option could be useful for identifying the running operating system, as there are a lot of VoIP devices that are running on a specific operating system, such as Cisco embedded.

You know what to do now. After footprinting and scanning, we need to enumerate the target. As you can see, when exploiting an infrastructure we generally follow the same methodological steps.

Banner grabbing is a well-known technique in enumeration, and the first step to enumerate a VoIP infrastructure is by starting a banner grabbing move. In order to do that, using the Netcat utility would help you grab the banner easily, or you can simply use the Nmap script named banner:

nmap -sV --script=banner 

For a specific vendor, there are a lot of enumeration tools you can use; EnumIAX is one of them. It is a built-in enumeration tool in Kali Linux to brute force Inter-Asterisk Exchange protocol usernames:

Automated Corporate Enumerator (ACE) is another built-in enumeration tool in Kali Linux:

svmap is an open source built-in tool in Kali Linux for identifying SIP devices. Type svmap -h and you will get all the available options for this amazing tool:

VoIP attacks

By now, you have learned the required skills to perform VoIP footprinting, scanning, and enumeration. Let’s discover the major VoIP attacks. VoIP is facing multiple threats from different attack vectors.

Denial-of-Service

Denial-of-Service (DoS) is a threat to the availability of a network. DoS could be dangerous too for VoIP, as ensuring the availability of calls is vital in modern organizations. Not only the availability but also the clearness of calls is a necessity nowadays. To monitor the QoS of VoIP, you can use many tools that are out there; one of them is CiscoWorks QoS Policy Manager 4.1:

To measure the quality of VoIP, there are some scoring systems, such as the Mean Opinion Score (MOS)  or the R-value based on several parameters (jitter, latency, and packet loss). Scores of the mean opinion score range from 1 to 5 (bad to very clear) and scores of R-value range from 1 to 100 (bad to very clear). The following screenshot is taken from an analysis of an RTP packet downloaded from the Wireshark website:

You can also analyze the RTP jitter graph:

VoIP infrastructure can be attacked by the classic DoS attacks. We saw some of them previously:

  • Smurf flooding attack
  • TCP SYN flood attack
  • UDP flooding attack

One of the DoS attack tools is iaxflood. It is available in Kali Linux to perform DoS attacks. IAX stands for  Inter-Asterisk Exchange.

Open a Kali terminal and type  iaxflood   :

The VoIP infrastructure can not only be attacked by the previous attacks attackers can perform packet Fragmentation and Malformed Packets to attack the infrastructure, using fuzzing tools.

Eavesdropping

Eavesdropping is one of the most serious VoIP attacks. It lets attackers take over your privacy, including your calls. There are many eavesdropping techniques; for example, an attacker can sniff the network for TFTP configuration files while they contain a password. The following screenshot describes an analysis of a TFTP capture:

Also, an attacker can harvest phone numbers and build a valid phone numbers databases, after recording all the outgoing and ongoing calls. Eavesdropping does not stop there, attackers can record your calls and even know what you are typing using the Dual-Tone Multi-Frequency (DTMF). You can use the DTMF decoder/encoder from this link http://www.polar-electric.com/DTMF/:

Voice Over Misconfigured Internet Telephones (VOMIT) is a great utility to convert Cisco IP Phone conversations into WAV files. You can download it from its official website http://vomit.xtdnet.nl/:

SIP attacks

Another attacking technique is SIP rogues. We can perform two types of SIP rogues. From an attacker’s perspective, we can implement the following:

  • Rogue SIP B2BUA: In  this attacking technique, the attacker mimics SIP B2BUA:

  • SIP rogue as a proxy: Here, the attacker mimics a SIP proxy:

 

SIP registration hijacking

SIP registration hijacking is a serious VoIP security problem. Previously, we saw that before establishing a SIP session, there is a registration step. Registration can be hijacked by attackers. During a SIP registration hijacking attack, the attacker disables a normal user by a Denial of Service, for example, and simply sends a registration request with his own IP address instead of that users because, in SIP, messages are transferred clearly, so SIP does not ensure the integrity of signalling messages:

If you are a Metasploit enthusiast, you can try many other SIP modules. Open a Metasploit console by typing msfconsole and search SIP modules using search SIP:

To use a specific SIP module, simply type use . The following interface is an example of SIP module usage:

Spam over Internet Telephony

Spam over Internet Telephony (SPIT), sometimes called Voice spam, is like email spam, but it affects VoIP. To perform a SPIT attack, you can use a generation tool called spitter.

Embedding malware

Malware is a major threat to VoIP infrastructure. Your insecure VoIP endpoints can be exploited by different types of malware, such as Worms and VoIP Botnets.

Softphones are also a highly probable target for attackers. Compromising your softphone could be very dangerous because if an attacker exploits it, they can compromise your VoIP network. Malware is not the only threat against VoIP endpoints. VoIP firmware is a potential attack vector for hackers. Firmware hacking can lead to phones being compromised.

Viproy – VoIP penetration testing kit

Viproy VoIP penetration testing kit (v4)  is a VoIP and unified communications services pentesting tool presented at Black Hat Arsenal USA 2014 by Fatih Ozavci:

To download this project, clone it from its official repository, https://github.com/fozavci/viproy-voipkit:

# git clone https://github.com/fozavci/viproy-voipkit.

The following project contains many modules to test SIP and Skinny protocols:

To use them, copy the lib, modules, and data folders to a Metasploit folder in your system.

Thus, in  this article, we demonstrated how to exploit the VoIP infrastructure. We explored the major VoIP attacks and how to defend against them, in addition to the tools and utilities most commonly used by penetration testers.

If you’ve enjoyed reading this, do check out Advanced Infrastructure Penetration Testing to discover post-exploitation tips, tools, and methodologies to help your organization build an intelligent security system.

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