How does caller ID spoofing work?

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How Caller ID Spoofing Works Technically:
The ability to spoof Caller ID stems from the design of telecommunication networks and the protocols they use to set up calls.

Traditional PSTN (Public Switched Telephone Network) and SS7:

The traditional telephone network relies on a signaling system called SS7 (Signaling System No. 7) to set up, manage, and tear down calls. When a call is initiated, the originating telephone exchange sends various signaling messages across the network to the destination exchange.
One crucial piece of information carried in these SS7 messages is the Calling Party Number (CPN), which is intended to be the caller's actual phone number.
Historically, SS7 networks were built on a foundation of trust, assuming that all interconnected carriers would transmit legitimate CPNs. There was no robust, inherent mechanism within SS7 to cryptographically authenticate that the CPN being sent truly belonged to the originating caller.
Fraudsters can exploit this lack of strong authentication by using specialized equipment, gaining access to compromised Private Branch Exchange (PBX) systems, or leveraging the services of rogue or unregulated telecom carriers (often in other countries) that allow manipulation of the CPN field before injecting the call into the SS7 network. The manipulated CPN then propagates through the network to the recipient's phone.
VoIP (Voice over Internet Protocol) and SIP:

With the increasing shift to VoIP, where calls are transmitted romania phone number list over the internet, caller ID spoofing has become even more accessible and prevalent. VoIP uses protocols like SIP (Session Initiation Protocol) to initiate and manage calls.
In a SIP call, the caller's information, including the phone number, is conveyed in various headers within the SIP messages (e.g., the "From" header or "P-Asserted-Identity" header).
Many VoIP service providers, especially those offering "wholesale VoIP" or those without strict validation processes, allow users to set virtually any value in these headers. Attackers can sign up with such providers or use open-source VoIP software (like Asterisk or FreeSWITCH) to easily manipulate the caller ID information they transmit.
When a VoIP call with a spoofed Caller ID then hits a gateway to the traditional PSTN, that gateway often simply passes through the Caller ID information it received from the VoIP side, effectively injecting the false number into the SS7 network.
How Attackers Leverage Spoofing:
Vishing Scams: This is the primary use. Scammers spoof numbers of banks, government agencies (e.g., NBR, police), local businesses, or even local numbers (neighbor spoofing) to increase the likelihood of the victim answering the call and trusting the imposter. The goal is to extract personal data, money, or coerce actions.
Harassment and Pranks: Individuals can use spoofing to conceal their identity for malicious harassment or practical jokes.
Evading Detection: By constantly changing spoofed numbers, fraudsters make it harder for victims to block them or for law enforcement to trace them.
Why it's a Problem:
The ease of spoofing undermines the Caller ID system, eroding trust in phone calls and making it significantly harder for individuals to distinguish legitimate calls from scams. This makes people more vulnerable to financial fraud, identity theft, and other malicious activities.

Combating Spoofing (STIR/SHAKEN):
To combat widespread Caller ID spoofing, telecommunications industries globally are adopting standards like STIR/SHAKEN (Secure Telephone Identity Revisited/Signature-based Handling of Asserted Information Using Tokens). This framework digitally signs and verifies the caller ID information for IP-based voice calls, allowing receiving networks to authenticate that the call's origin is legitimate and that the Caller ID has not been tampered with. While its full implementation is ongoing and primarily focused on IP-based calls, it represents a significant step towards restoring trust in Caller ID.