• Home
  • Cyber Crime
  • Cyber warfare
  • APT
  • Data Breach
  • Deep Web
  • Digital ID
  • Hacking
  • Hacktivism
  • Intelligence
  • Internet of Things
  • Laws and regulations
  • Malware
  • Mobile
  • Reports
  • Security
  • Social Networks
  • Terrorism
  • ICS-SCADA
  • POLICIES
  • Contact me
MUST READ

Qilin ransomware claimed responsibility for the attack on the beer giant Asahi

 | 

DragonForce, LockBit, and Qilin, a new triad aims to dominate the ransomware landscape

 | 

DraftKings thwarts credential stuffing attack, but urges password reset and MFA

 | 

Redis patches 13-Year-Old Lua flaw enabling Remote Code Execution

 | 

U.S. CISA adds Synacor Zimbra Collaboration Suite (ZCS) flaw to its Known Exploited Vulnerabilities catalog

 | 

GoAnywhere MFT zero-day used by Storm-1175 in Medusa ransomware campaigns

 | 

CrowdStrike ties Oracle EBS RCE (CVE-2025-61882) to Cl0p attacks began Aug 9, 2025

 | 

Discord discloses third-party breach affecting customer support data

 | 

Oracle patches critical E-Business Suite flaw exploited by Cl0p hackers

 | 

LinkedIn sues ProAPIs for $15K/Month LinkedIn data scraping scheme

 | 

Zimbra users targeted in zero-day exploit using iCalendar attachments

 | 

Reading the ENISA Threat Landscape 2025 report

 | 

Ghost in the Cloud: Weaponizing AWS X-Ray for Command & Control

 | 

SECURITY AFFAIRS MALWARE NEWSLETTER ROUND 65

 | 

Security Affairs newsletter Round 544 by Pierluigi Paganini – INTERNATIONAL EDITION

 | 

GreyNoise detects 500% surge in scans targeting Palo Alto Networks portals

 | 

U.S. CISA adds Smartbedded Meteobridge, Samsung, Juniper ScreenOS, Jenkins, and GNU Bash flaws to its Known Exploited Vulnerabilities catalog

 | 

ShinyHunters Launches Data Leak Site: Trinity of Chaos Announces New Ransomware Victims

 | 

ProSpy, ToSpy malware pose as Signal and ToTok to steal data in UAE

 | 

Google warns of Cl0p extortion campaign against Oracle E-Business users

 | 
  • Home
  • Cyber Crime
  • Cyber warfare
  • APT
  • Data Breach
  • Deep Web
  • Digital ID
  • Hacking
  • Hacktivism
  • Intelligence
  • Internet of Things
  • Laws and regulations
  • Malware
  • Mobile
  • Reports
  • Security
  • Social Networks
  • Terrorism
  • ICS-SCADA
  • POLICIES
  • Contact me
  • Home
  • Cyber Crime
  • Hacking
  • Security
  • Exploring the Telephony Denial of Service (TDoS) Q&A

Exploring the Telephony Denial of Service (TDoS) Q&A

Pierluigi Paganini January 30, 2014

Interviewed with Mark Collier, CTO and VP of Engineering at Securelogix to better understand the topic of Telephony Denial of Service (TDoS).

I briefly interviewed Mark Collier, CTO and VP of Engineering at SecureLogix (Www.securelogix.com) on the topic of Telephony Denial of Service (TDoS). Mark just completed the Hacking Exposed: UC and VoIP book, which covers TDoS and related topics. Mark has been working in this space for some 20 years, maintains the www.voipsecurityblog.com blog on this topic, and is a frequent speaker at conferences on this topic.

Hi Mark, I have seen a lot of press on Telephony Denial of Service (TDoS). What is it?

Telephony Denial of Service or TDoS is a flood of unwanted, malicious inbound calls. The calls are usually into a contact center or other part of an enterprise, which depends heavily on voice service. Examples are financial contact centers, Intensive Care Units (ICUs) and emergency rooms in hospitals, and public services such as 911. The intent of the attacker is disruption or financial gain through extortion.

TDOS

As far as the press is concerned, let me add a couple of articles on the topic that could be interesting for my readers:

  • New York Times: Swindlers Use Telephones, With Internet’s Tactics
  • Los Angeles Times: VoIP phone hackers pose public safety threat
  • Brian Krebs: DHS Warns of ‘TDos’ Extortion Attacks on Public Emergency Networks
  • VoIPSA: Voice of VOIPSA
     

Can you give some examples of real world attacks?

The “Payday loan SCAM” is probably the best known. In this scam, the attacker obtained a list of individuals who have taken out short-term “payday” loans. The attacker calls the victim’s place of business, states that the individual has not paid their loan (which is often true), and that if they don’t pay, the attacker will embarrass and harass them by repeatedly calling their place of business. This attack has progressed to where the attackers are also just calling ICUs and emergency rooms and making the same threat. When the victim or enterprise refuses to pay, which is what they should do, they are hit with a barrage of calls. The calls are generated through a combination of cheap labor pools and automated call generation. Amazingly, over $5,000,000 has been paid out on this scam. The attacker provides a pre-paid, anonymous debit card, upon which the victim adds funds.

There have been a number of attacks and press information about attacks against emergency services. Some intentional and some unintentional (a famous rapper sent a tweet to his 600,000 followers to call in complaints to the local sheriffs office, when bled over to the emergency services). We have also worked with multiple financial enterprises, whose contact centers were victims of TDoS or call pumping attacks (which created a TDoS condition).

What makes these attacks possible?

It is very easy to anonymously generate calls into the public voice network. It is very easy to spoof your calling number, so the victims don’t know where the calls are coming from. Attackers can use cheap labor pools and hard-to-trace VoIP applications such as Skype to generate the calls. More likely though, the attackers can use a variety of automated techniques to generate the calls. With inexpensive SIP access to the network, free and powerful IP PBX software like Asterisk, call generators, the ability to spoof the calling number, and ready information on the Internet, make it easy to generate automated TDoS. The Hacking Exposed: UC and VoIP book covers this process in detail, including a sample attack. Turnkey TDoS tools such as those discussed by Dancho Danchev can also be used.

What do you recommend enterprises do about these attacks?

The right place in an enterprise to address these threats is on the perimeter, before they saturate the trunks and overwhelm the internal IP PBX or contact center system. Keep in mind that most of the attacks enter an enterprise through TDM trunks. While SIP trunks are being deployed rapidly, they account for perhaps 10-15% of the overall trunks, so any solution has to address both. IP PBXs have some basic capability, but it is very limited. Session Border Controllers (SBCs) can provide some mitigation, but they only work for SIP and really only look at the underlying packets, not the malicious calls. Companies like SecureLogix offer application-level security solutions, which monitor all types of trunks, and look at all the signaling and media, to identify the calls that are part of the TDoS attack and remove them from the network.

Pierluigi Paganini

(Security Affairs –  TDOS, cybercrime)


facebook linkedin twitter

Cybercrime DOS Hacking PBX SIP Skype TDoS Telephony Denial of Service VOIP

you might also like

Pierluigi Paganini October 08, 2025
Qilin ransomware claimed responsibility for the attack on the beer giant Asahi
Read more
Pierluigi Paganini October 08, 2025
DragonForce, LockBit, and Qilin, a new triad aims to dominate the ransomware landscape
Read more

leave a comment

newsletter

Subscribe to my email list and stay
up-to-date!

    recent articles

    Qilin ransomware claimed responsibility for the attack on the beer giant Asahi

    Cyber Crime / October 08, 2025

    DragonForce, LockBit, and Qilin, a new triad aims to dominate the ransomware landscape

    Cyber Crime / October 08, 2025

    DraftKings thwarts credential stuffing attack, but urges password reset and MFA

    Security / October 08, 2025

    Redis patches 13-Year-Old Lua flaw enabling Remote Code Execution

    Security / October 08, 2025

    U.S. CISA adds Synacor Zimbra Collaboration Suite (ZCS) flaw to its Known Exploited Vulnerabilities catalog

    Hacking / October 07, 2025

    To contact me write an email to:

    Pierluigi Paganini :
    pierluigi.paganini@securityaffairs.co

    LEARN MORE

    QUICK LINKS

    • Home
    • Cyber Crime
    • Cyber warfare
    • APT
    • Data Breach
    • Deep Web
    • Digital ID
    • Hacking
    • Hacktivism
    • Intelligence
    • Internet of Things
    • Laws and regulations
    • Malware
    • Mobile
    • Reports
    • Security
    • Social Networks
    • Terrorism
    • ICS-SCADA
    • POLICIES
    • Contact me

    Copyright@securityaffairs 2024

    We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept All”, you consent to the use of ALL the cookies. However, you may visit "Cookie Settings" to provide a controlled consent.
    Cookie SettingsAccept All
    Manage consent

    Privacy Overview

    This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities...
    Necessary
    Always Enabled
    Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
    Non-necessary
    Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.
    SAVE & ACCEPT