A2P SMS DoS Attacks: Strategies for Maintaining MNOs Firewall Integrity

An A2P SMS DoS (Denial of Service) attack can significantly impact the SMS firewall within a Mobile Network Operator (MNO). SMS firewalls are designed to filter and manage SMS traffic, protecting the network from all kinds of “bypass” nefarious activities, such as terminating messages through unauthorized or unofficial routes.

However, during a DoS attack, the volume and nature of the traffic can challenge the firewall’s capabilities. Next, let’s showcase the mechanics of an A2P SMS DoS attack by taking a hypothetical example.

Example A2P SMS DoS Attack Scenario

A firewall (FW) is installed at MNO premises with a total capacity of 500 transactions per second (TPS). The firewall, regardless if managed by the MNO, the firewall service provider, or an exclusive partner, receives traffic from various carriers. If the load exceeds 500 TPS, the FW becomes overloaded which can lead to service downtime. Fraudsters (connected directly or indirectly to the FW) can attempt to artificially overload the FW to then bypass production traffic unmonetized – a repeatable bypass that cannot be prevented by firewall rules. 

In worst-case scenarios, it can even take the entire network down. A Denial of Service (DOS) attack can also have a direct impact on the MNO’s Home Location Register (HLR).

Here’s how such an attack can affect the SMS firewall:

The effects of an SMS DoS Attack on an SMS firewall

A DoS attack can negatively impact a firewall in multiple ways. When an SMS firewall is overwhelmed by a DoS attack, it not only faces difficulties in processing the high volume of incoming messages but also risks the integrity and reliability of the entire network. The sheer volume of malicious traffic can strain the firewall’s resources, degrade its performance, and lead to significant service disruptions. 

The attack can exploit weaknesses in the firewall’s filtering mechanisms, allowing harmful messages to slip through, while simultaneously causing legitimate traffic to be delayed or lost. Such an attack undermines the overall security and operational efficiency of the Mobile Network Operator (MNO), making it crucial to understand and mitigate these potential impacts.

Let’s break it down.

1. Overloading the Firewall

Overloading can cripple the firewall’s responsiveness, making it a prime target for further exploitation by persistent attackers. The increased traffic can cause significant slowdowns, allowing cybercriminals to time their actions for maximum disruption.

• Excessive Traffic: An A2P SMS DoS attack floods the firewall with a high volume of SMS messages, overwhelming its processing capacity.
• Delayed Processing: The firewall may struggle to process and filter all incoming messages in real-time, leading to delays and backlogs.

2. Resource Exhaustion

Resource exhaustion not only disrupts service but also opens the door to secondary attacks while the system is down. Once the firewall’s resources are depleted, recovery times can be lengthy, further exposing the network to additional threats.

• CPU and Memory Strain: The high volume of messages consumes significant CPU and memory resources, potentially exhausting the firewall’s capacity.
• System Crashes: In severe cases, the strain can cause the firewall to crash or become unresponsive, compromising the MNO’s ability to filter and route messages.

3. Filter Inefficiency

Filter inefficiency during an attack can erode user trust as spam and fraud messages slip through more frequently. The compromised ability to differentiate between legitimate and malicious messages can lead to a breakdown in communication integrity.

• Bypassing Filters: Let’s take the infamous template spoofing attack for example. Bad actors might send messages that mimic legitimate traffic. It becomes increasingly difficult for the firewall to distinguish between normal and malicious messages. This could potentially allow harmful messages to pass through.
• Increased False Positives/Negatives: The overload can increase false positives (legitimate messages being blocked) and false negatives (malicious messages getting through).

4. Service Disruption

Service disruptions, such as delayed or lost messages, can lead to significant user dissatisfaction and potential revenue loss. Prolonged service issues may also cause users to switch providers, harming the MNO’s market position and reputation.

• Message Delays: Legitimate SMS traffic experiences significant delays due to the firewall’s inability to process messages quickly enough.
• Message Loss: If the firewall’s buffers overflow, some messages may be dropped, causing the loss of legitimate and attack traffic.

5. Compromised Security

Compromised security undermines the MNO’s overall defensive posture, making it vulnerable to a range of malicious activities. The weakened filtering capabilities can provide a gateway for more sophisticated and damaging attacks, escalating the overall risk.

• Reduced Filtering Accuracy: The precision of filtering rules and algorithms may degrade under heavy load, reducing the firewall’s effectiveness in blocking spam, fraud, and other malicious content.
• Vulnerability Exploitation: Attackers might exploit the firewall’s overload to introduce vulnerabilities or bypass existing security measures.

Mitigation Strategies

Implementing robust mitigation strategies is crucial for safeguarding SMS firewalls against DoS attacks. These strategies ensure the network remains resilient, maintaining service integrity and security by effectively managing and distributing traffic loads. 

Adopting scalable solutions allows the system to handle unexpected spikes, while advanced analytics enhance the detection of anomalous patterns indicative of attacks. Collaborative efforts with security providers and industry partners fortify the MNO’s defenses, enabling swift adaptation to evolving threats and ensuring continuous protection against sophisticated attacks.

Let’s dive a little deeper.

Scalable Infrastructure

Ensuring a scalable infrastructure is deployed is crucial to seamlessly manage fluctuating traffic volumes without disrupting service. This adaptive capability maintains network resilience and responsiveness, crucial during peak usage periods.

• Load Balancing: Distribute incoming SMS traffic across multiple firewalls or servers to balance the load and prevent any single point of failure.
• Auto-scale cluster: Utilize cloud-based SMS filtering solutions that can scale resources dynamically to handle traffic spikes.

Throughput Limiting and Throttling

Effective rate limiting and throttling mechanisms are essential in preventing system overload and maintaining optimal performance. By regulating message flow, these two strategies not only protect against high-volume attacks but also sustain consistent service delivery across the network.

• Per Source Limits: Implement rate limiting on the number of messages that can be sent from a single source or IP address within a given time frame.
• Throttling: Gradually reduce the processing rate for sources that exceed normal traffic patterns to mitigate the impact of high-volume attacks.

Advanced Traffic Analysis

Traffic analysis is a sure way to swiftly detect and respond to potential threats. Leveraging machine learning algorithms enables real-time identification and mitigation of suspicious activities, bolstering overall network security.

• Anomaly Detection: Machine learning and advanced analytics are used to detect unusual traffic patterns indicative of a DoS attack.
• Real-time Monitoring: Continuously monitor traffic in real-time to identify and respond to potential attacks swiftly.

Robust Filtering Rules

Through adaptive filtering rules and sophisticated content analysis, the firewall can effectively fortify defenses. This will minimize the risk of false positives and bolster threat detection capabilities.

• Dynamic Rules: Employ adaptive filtering rules that can adjust based on current traffic conditions and attack patterns.
• Content Analysis: Analyse message content for patterns typical of DoS attacks, such as repeated messages or characteristic payloads.

Collaboration with Security Providers

Last, but not least, we need to consider various types of collaborations with other MNOs and security providers. This cooperative approach strengthens the network’s resilience against evolving threats, ensuring a proactive security posture across the board.

• DoS Protection Services: Partner with specialized services offering enhanced mitigation capabilities.
• Threat Intelligence Sharing: Collaborate with other MNOs and security organizations to share threat intelligence and best practices.

Conclusion

Safeguarding SMS firewalls requires proactive measures and robust defenses. By implementing all or just a combination of the outlined mitigation strategies, MNOs can fortify their networks against disruptive threats. These will not only ensure service integrity and security but also enable rapid adaptation to emerging attack vectors. 

For expert consultancy on defending against A2P SMS DoS attacks and enhancing network resilience, consider partnering with GTC. Together, we can secure your infrastructure and maintain uninterrupted communication services amidst evolving cybersecurity challenges. Need help? Hit us up here.