Ahmet Göker
11 min readApr 28, 2022


Hey there,

Welcome back to this blog post. Today, we delve into a timeless yet persistently recognized vulnerability, one that remains a potent weapon in the arsenal of cyber attackers. This enduring concept has not lost its relevance over the years and continues to be a matter of concern within the field of cybersecurity.


SS7 is a foundational and crucial component of the telecommunications infrastructure, primarily designed to handle the signaling and control functions in the Public Switched Telephone Network (PSTN) and various other telecommunication networks. Here are some key aspects of SS7:

Call Establishment:

One of the core functions of SS7 is to facilitate the establishment of telephone calls. It handles the exchange of signaling messages between network elements to set up, manage, and terminate calls.

2. Billing:

SS7 plays a vital role in billing and charging for telecommunication services. It assists in tracking call durations, routing information, and other call-related data necessary for accurate billing.

3. Routing:

Routing of calls within the PSTN and between different telecommunication networks relies heavily on SS7. It ensures that calls reach their intended destinations efficiently.

4. Information Exchange:

Beyond voice calls, SS7 supports the exchange of various information types, including text messages, multimedia messages, and service-specific data.

5. Network Management:

SS7 aids in the management and maintenance of the telecommunications network. It allows for remote configuration and monitoring of network elements.


Many mobile operators have taken proactive measures to fortify their SS7 perimeters by initiating critical steps, such as the reconfiguration of network equipment and the deployment of SMS home routing solutions. These measures indeed represent significant strides in safeguarding their networks against rudimentary SS7 attacks. However, it is imperative to acknowledge that while these initial steps form a foundational defense, they may fall short in providing comprehensive protection.

In the realm of cybersecurity, the effectiveness of security measures is subject to relentless scrutiny and adaptation. Security audits and assessments consistently reveal that even with the implementation of these security mechanisms, vulnerabilities persist. The alarming reality is that certain SS7 attacks have demonstrated the capability to circumvent these safeguards, evading detection and compromising network integrity.

Moreover, the sophistication of real-world SS7 attacks often transcends the boundaries of simplicity. Attackers have developed more subtle and insidious strategies, making their incursions exceedingly challenging to identify at an early stage. These stealthy tactics may involve the use of advanced evasion techniques, obfuscation methods, or targeted approaches that specifically exploit weaknesses in a network’s defenses.

In essence, while the fortification of SS7 perimeters through reconfiguration and SMS home routing is undoubtedly a commendable stride toward security enhancement, it must be regarded as the initial layer of protection. To truly safeguard against the evolving landscape of SS7 threats, network operators must adopt a holistic security posture that combines robust infrastructure defenses with vigilant monitoring, anomaly detection, and threat intelligence. In this dynamic cybersecurity landscape, the quest for network resilience is an ongoing endeavor, demanding continuous adaptation and innovation to thwart the relentless pursuit of attackers.


“Armed with access to the SS7 network and armed with a victim’s phone number, an attacker wields a formidable arsenal of capabilities, each carrying the potential for profound intrusion and disruption. The SS7 network, designed with the noble intention of facilitating seamless telecommunications, inadvertently becomes a double-edged sword in the hands of malicious actors.

Here are some of the alarming capabilities an attacker can harness:

Eavesdropping on Conversations:

With the ability to intercept voice calls, an attacker can surreptitiously listen to private conversations, breaching the sanctity of personal communication and potentially exposing sensitive information.

2. Pinpointing Geolocation:

By exploiting the SS7 network’s inherent tracking capabilities, attackers can precisely determine a victim’s location, turning every mobile device into a potential surveillance beacon.

3. Intercepting Messages for Financial Gain:

Attackers can intercept SMS messages, including those containing one-time passwords (OTPs), which are often used for mobile banking and two-factor authentication. This enables unauthorized access to financial services, leading to fraudulent transactions and unauthorized account access.

4. Manipulating USSD Commands:

Unstructured Supplementary Service Data (USSD) commands, typically used for services like balance inquiries and prepaid top-ups, can be sent to billable numbers, incurring charges on the victim’s behalf, leading to financial losses.

5. Penetrating the SS7 Network:

While access to the SS7 network is not a straightforward endeavor, attackers with sufficient resources and determination can find avenues to penetrate it. In some countries with lax regulations, obtaining an operator’s license may be relatively accessible. Alternatively, the black market offers a shadowy marketplace where access to the SS7 network can be purchased from unscrupulous operators for a substantial sum, often several thousand dollars.

The commodification of SS7 access on the black market underscores the dire need for heightened cybersecurity awareness and robust safeguards. While regulatory bodies and network operators must play a pivotal role in bolstering SS7 security, individuals must also exercise vigilance in safeguarding their personal information and adopting security measures such as two-factor authentication apps and encrypted messaging platforms.

In this landscape, where the SS7 network’s expansive capabilities meet the ambitions of attackers, a collective effort is essential to erect formidable defenses that can repel these incursions, protecting the privacy and security of individuals and organizations alike.”


Malefactors with a keen understanding of SS7 vulnerabilities recognize that the efficacy of security systems often hinges on the meticulous scrutiny of network configurations, particularly those that are not immediately apparent. Within the complex tapestry of telecommunications infrastructure, certain operators may hold the belief that they have taken the necessary precautions by implementing SMS Home Routing solutions and configuring their core equipment to block Category 1 messages. However, this sense of security may be a precarious illusion.

  1. The Illusion of Security:

Operators may perceive their networks as fortified when they have taken these initial steps. SMS Home Routing, for instance, is a multifaceted hardware and software solution designed to facilitate the proxying of confidential subscriber identifiers and equipment addresses when handling incoming texts from external connections. This solution, on the surface, appears to offer robust protection against various SS7 threats.

2. Bypassing Initial Protections:

Despite the implementation of such measures, experienced malefactors can skillfully navigate the labyrinth of SS7 intricacies. These attackers understand that while SMS Home Routing and message categorization can thwart certain types of attacks, they are not impervious to exploitation. Attack vectors that do not rely on obtaining an International Mobile Subscriber Identity (IMSI), such as those targeting network vulnerabilities or utilizing advanced evasion techniques, may persist as potential threats.

3. The Quest for IMSI:

Obtaining an IMSI is often considered a crucial element in conducting more insidious SS7 attacks. While it may be perceived as a formidable barrier, it is not an insurmountable one for determined attackers. IMSIs, although guarded, are not invincible, and crafty malefactors can devise strategies to infiltrate and glean these vital identifiers.

In essence, the concept of security in the realm of SS7 networks is a multifaceted and dynamic challenge. Operators should acknowledge that while initial security measures such as SMS Home Routing are invaluable components of a defense strategy, they must be part of a broader and continuously evolving security posture. This posture should encompass comprehensive monitoring, threat intelligence, intrusion detection systems, and regular security audits. In the ever-evolving landscape of cybersecurity, vigilance and adaptability are paramount, as attackers persistently seek vulnerabilities that may not be evident at first sight.”


One of the most popular attacks on SS7 networks is location tracking. A request for subscriber location is sent via SS7 networks, the response includes the base station identify. Each base station has specific geographic coordinates and covers a particular area. Because of urban density, the coverage are in a city ranges from tens to hundreds of meters. An attacker can make use of these mobile network peculiarities to generate location requests, as well as to locate the base station by its identity using.

Normally, a mobile device chooses a base station with the best radio conditions during a transaction. Therefore, the mobile device should interchange signals with the network. The malefactor can use a so-called silent SMS to initiate a hidden transaction with the target subscriber. However, the information about these messages is available in the subscriber’s account. A more effective way to hide a transaction is to use silent USSD notifications. Although such transactions are not registered by the billing system


in the context of SS7 networks refers to a sophisticated method of intercepting and accessing text messages (SMS) without alerting the target or the network operator to the interception. This type of interception can be challenging to detect because it doesn’t involve the physical alteration of a mobile device or network infrastructure. Instead, it exploits vulnerabilities within the SS7 protocol itself.

Background on SS7 Networks:

SS7 is a set of telephony signaling protocols used in the telecommunications industry to set up and tear down telephone calls, exchange text messages, and manage other communication services. It is used by cellular networks, landline networks, and various other telecommunication systems.

2. SMS in SS7 Networks:

SMS is a widely used service in SS7 networks for various purposes, including one-time password (OTP) delivery, password recovery for online services, and even for two-factor authentication (2FA). When you receive an SMS, it is routed through the SS7 network to your mobile device.

3. SMS Interception Attack:

The SMS interception attack you mentioned involves an attacker attempting to intercept SMS messages destined for a specific target subscriber. Here’s a step-by-step breakdown of how this attack works:

a.Registering a Fake Subscriber:

The attacker starts by setting up a “fake” subscriber in the SS7 network. This involves using specialized equipment and techniques to create a subscriber profile that appears legitimate to the network.

b. Simulating Roaming:

The attacker simulates the fake subscriber as if they are roaming in a visited network. In the context of SS7, when a subscriber roams to a different network, the Home Location Register (HLR) keeps track of their location for call and message routing purposes.

c. HLR Records:

The HLR, a core component of the SS7 network, maintains records of subscriber locations. When someone tries to send an SMS to the target subscriber, the HLR directs the message to the subscriber’s current location, which the attacker has manipulated to point to the fake network.

d. Failed Delivery Attempts:

When someone tries to send an SMS to the target subscriber, the first delivery attempt fails because the HLR directs it to the fake network. The attacker can repeat this process to make subsequent SMS delivery attempts fail as well.

e. Interception and Redirection:

If the attacker has control over the network element that masquerades as a new Mobile Switching Center (MSC), they can intercept the terminating SMS messages. Once intercepted, the attacker can either read the message or redirect it to their desired destination, effectively capturing sensitive information.

4. Implications and Risks:

This attack poses significant risks, as it allows attackers to intercept sensitive information such as OTPs, password reset codes, and other critical SMS-based security measures. They can potentially gain unauthorized access to a victim’s accounts or impersonate them.

5. Countermeasures:

To mitigate the risks associated with SMS interception attacks on SS7 networks, telecommunications providers and organizations can implement various security measures, including:

Network Monitoring: Continuously monitoring network traffic for suspicious activity.
— Authentication Protocols: Implementing stronger authentication and encryption protocols to protect SS7 signaling messages.
— Firewall and Access Controls: Deploying firewalls and access controls to prevent unauthorized access to network elements.
— Subscriber Validation: Verifying subscriber identities through multiple channels to prevent fake subscriber registrations.

It’s important to note that while these countermeasures can enhance security, SS7 networks continue to face evolving threats, and ongoing vigilance and security enhancements are necessary to protect against such attacks. Additionally, some telecommunication providers are transitioning to more secure protocols, such as Diameter, to address the vulnerabilities associated with SS7.


I acknowledge that delving into the intricate subject matter of SS7-based telecommunications attacks can be daunting, particularly for individuals who lack prior experience in signaling, telecommunications, or the realm of telecom security. It is crucial to recognize that comprehending this topic necessitates a comprehensive understanding of the underlying protocols, vulnerabilities, and countermeasures. As a newcomer to this field, I embarked on this research journey with an eagerness to explore and share my findings, even though I may not have fully grasped its complexities at the outset.

I wholeheartedly recommend conducting thorough and exhaustive research, encompassing in-depth explanations and intricate details, to gain a nuanced comprehension of SS7 attacks. While I aspired to share this blog post with you, I must admit that I may not have been entirely prepared to do so. However, I remain receptive to any inquiries and am committed to addressing questions in a structured and informative manner. It is my aspiration to provide accurate and well-considered responses, even as I acknowledge my status as a newcomer in this specialized field.

In conclusion, I encourage fellow researchers and enthusiasts to embark on this learning journey with a steadfast commitment to acquiring knowledge and expertise. Navigating the multifaceted terrain of SS7-based attacks requires diligent study and a commitment to understanding the intricacies of the subject matter.

İntellingence agencies?

Intelligence agencies and government entities have been reported to have used SS7 vulnerabilities for various purposes, including surveillance and intelligence gathering. However, it’s important to clarify that these agencies typically have legal and regulatory frameworks that allow them to access and use SS7 data for national security or law enforcement purposes under specific circumstances.

The use of SS7 for intelligence or surveillance purposes is a contentious and sensitive issue. When such practices come to light, they often raise concerns about privacy, civil liberties, and the potential for misuse of surveillance capabilities.

In recent years, there has been increased scrutiny of SS7 security and the need to protect telecommunications networks from unauthorized access and exploitation, whether by intelligence agencies, cybercriminals, or other malicious actors. Telecommunications providers and regulatory authorities are working to implement stronger security measures to mitigate SS7 vulnerabilities and protect user privacy.

It’s essential to recognize that the use of SS7 for intelligence purposes is a complex and often controversial topic, and the specifics can vary from country to country based on their respective legal and regulatory frameworks. Public debates continue regarding the balance between national security interests and individual privacy rights in the context of SS7 and other telecommunications surveillance methods.

Thanks for reading this blog.



Ahmet Göker

🧑‍💻 Security Researcher || Sociologist