RPC: Network Protocol Explained

RPC ((Remote Procedure Call) sometimes called RPCP(Remote Procedure Call Protocol)) is a communication protocol used by computer systems to enable one system to request services or functions from another system over a network. It allows developers to build distributed applications, where components are spread across multiple computers, without needing to worry about the underlying network infrastructure.

What Is RPC

RPC simplifies the process of building distributed applications by allowing developers to create components that are spread across multiple computers, without needing to worry about the underlying network infrastructure.

The main components of RPC are:

1. Client: The system that makes the remote procedure call, requesting a service or function from the server.
2. Server: The system that provides the requested services or functions in response to the client’s call.
3. Stub: A piece of code that is generated automatically, allowing the client to call the remote procedure as if it were a local function. This helps in abstracting the complexities of network communication.
4. Remote Procedure: The actual function or service being requested by the client and executed by the server.

The RPC process typically involves these steps:

1. The client invokes a local function (the stub) that represents the remote procedure.
2. The stub serializes the function parameters into a standardized format, usually using a data serialization protocol.
3. The serialized data is sent over the network to the server, which receives the request.
4. The server deserializes the data and invokes the appropriate remote procedure with the provided parameters.
5. The server then serializes the results (if any) and sends them back to the client.
6. The client’s stub deserializes the results and returns them to the original local function call.

By enabling systems to request and execute procedures remotely, RPC facilitates the development of distributed applications and supports more efficient, scalable, and flexible software architectures.

The Purpose Of RPC

The main purpose of RPC is to facilitate communication and interaction between different computer systems, allowing them to request and execute procedures or services remotely over a network. RPC is essential for developing distributed applications, where components of the application are spread across multiple systems, providing several benefits:

1. Abstraction: RPC abstracts the complexities of network communication, allowing developers to call remote procedures as if they were local functions. This simplifies the development process and makes it easier to build distributed systems.
2. Scalability: Distributed applications built with RPC can easily scale by adding more systems or resources to handle increased workloads. This allows applications to grow and adapt to changing requirements without significant architectural changes.
3. Flexibility: RPC enables systems to be loosely coupled, meaning that components can be updated, replaced, or modified independently without affecting the entire application. This flexibility makes it easier to maintain and evolve distributed systems over time.
4. Fault tolerance and resilience: By distributing components across multiple systems, RPC-based applications can be designed to handle failures more effectively. If one system fails, other systems can continue to operate, and the failed system can be replaced or repaired without causing a complete system outage.
5. Resource optimization: RPC allows systems to share resources and services, enabling more efficient use of computing resources. For example, a computationally expensive service can be offloaded to a dedicated server, freeing up resources on the client systems.
6. Platform and language independence: Many RPC implementations support multiple programming languages and platforms, allowing developers to build distributed systems using the best tools for each component without worrying about compatibility issues.

In summary, the purpose of RPC is to enable efficient communication between computer systems over a network, simplifying the development of distributed applications and providing benefits such as scalability, flexibility, fault tolerance, resource optimization, and platform independence.

Benefits Of RPC

RPC offers several benefits when developing distributed applications, where components are spread across multiple computer systems. The key advantages of using RPC include:

1. Simplified development: RPC abstracts the complexities of network communication, allowing developers to call remote procedures as if they were local functions. This makes it easier to build and maintain distributed systems without needing in-depth knowledge of network protocols and communication details.
2. Scalability: Distributed applications built using RPC can be easily scaled by adding more systems or resources to handle increased workloads. This enables applications to grow and adapt to changing requirements without significant architectural changes.
3. Flexibility: RPC promotes loose coupling between systems, meaning that components can be updated, replaced, or modified independently without affecting the entire application. This flexibility makes it easier to maintain and evolve distributed systems over time.
4. Fault tolerance and resilience: By distributing components across multiple systems, RPC-based applications can be designed to handle failures more effectively. If one system fails, other systems can continue to operate, and the failed system can be replaced or repaired without causing a complete system outage.
5. Resource optimization: RPC allows systems to share resources and services, enabling more efficient use of computing resources. For example, a computationally expensive service can be offloaded to a dedicated server, freeing up resources on the client systems.
6. Platform and language independence: Many RPC implementations support multiple programming languages and platforms, allowing developers to build distributed systems using the best tools for each component without worrying about compatibility issues.
7. Interoperability: RPC protocols like XML-RPC, JSON-RPC, and gRPC facilitate communication between different systems, regardless of their underlying platforms or programming languages. This encourages seamless integration of diverse components, fostering cooperation and data exchange between various applications.

By providing these benefits, RPC enables developers to create distributed applications that are more scalable, flexible, fault-tolerant, and resource-efficient, while also simplifying development and maintenance processes.

Limitations Of RPC

Despite the numerous benefits of RPC in distributed application development, there are certain limitations associated with its use:

1. Latency and performance: Remote procedure calls over a network can introduce latency due to network delays, serialization, and deserialization processes. This can impact the performance of the application, especially when compared to local procedure calls.
2. Network reliability: RPC relies on network communication, making it susceptible to network-related issues such as congestion, packet loss, or downtime. This can result in failed or delayed remote procedure calls, affecting the overall application stability and reliability.
3. Security concerns: Exposing remote procedures over a network can introduce security vulnerabilities, as attackers may attempt to exploit these exposed interfaces. Developers must take care to implement proper authentication, authorization, and encryption mechanisms to secure the communication between the client and server systems.
4. Complexity in error handling: Error handling in RPC-based systems can be more complex than in local systems. Identifying and handling different types of errors, such as network errors, server-side errors, or parameter serialization errors, may require additional code and management.
5. State management: RPC is generally stateless, meaning that each remote procedure call is treated as an independent operation without any stored context. This can make it challenging to manage stateful operations or sessions between the client and server, often requiring additional mechanisms to handle state management.
6. Limited support for real-time communication: Traditional RPC implementations might not be well-suited for real-time communication, as they often rely on request-response patterns. However, modern implementations like gRPC offer bidirectional streaming capabilities that can address this limitation to some extent.
7. Compatibility issues: Some RPC implementations might not be compatible with each other, making it difficult to integrate components built with different RPC frameworks. However, more recent protocols like gRPC and JSON-RPC have improved interoperability between systems.

Despite these limitations, RPC remains a popular choice for developing distributed applications, as its benefits often outweigh the drawbacks. Developers can mitigate some of these limitations by carefully selecting the appropriate RPC framework, incorporating proper error handling and security mechanisms, and optimizing network performance.

How Does RPC Work

RPC is a communication protocol that enables a system (client) to request services or functions from another system (server) over a network. Here’s an overview of how RPC works in a typical distributed application:

1. Client-side stub: The client invokes a local function (the stub) that represents the remote procedure. This stub is a piece of code, usually auto-generated, that allows the client to call the remote procedure as if it were a local function.
2. Parameter serialization: The client-side stub serializes the function parameters into a standardized format using a data serialization protocol. Serialization converts the data into a format that can be transmitted over the network, such as XML or JSON.
3. Network communication: The serialized data is sent over the network to the server. The communication between the client and server usually takes place over a transport protocol, such as HTTP or TCP.
4. Server-side stub: The server receives the request and passes the serialized data to its corresponding server-side stub.
5. Parameter deserialization: The server-side stub deserializes the data, converting it back into the original data types and structures used by the remote procedure.
6. Remote procedure execution: The server invokes the appropriate remote procedure using the deserialized parameters. The remote procedure executes on the server, performing the requested operation and producing a result, if applicable.
7. Result serialization: If the remote procedure generates a result, the server-side stub serializes it into a standardized format, similar to the parameter serialization process.
8. Network communication: The serialized result is sent back over the network to the client-side stub.
9. Result deserialization: The client-side stub deserializes the result, converting it back into the original data type and structure expected by the client.
10. Return to the client: The deserialized result is returned to the original local function call made by the client. The client can then proceed with its operations using the result of the remote procedure call.

By following these steps, RPC enables systems to request and execute procedures remotely, simplifying the development of distributed applications and providing a seamless way for systems to interact over a network.

Security Concerns Of RPC

While RPC (Remote Procedure Call) provides a convenient way to develop distributed applications, it can introduce potential security concerns that developers should address:

1. Unauthorized access: Exposing remote procedures over a network can make them vulnerable to unauthorized access. Attackers may attempt to invoke these procedures without proper permission, compromising the security and integrity of the application.
2. Eavesdropping: Communication between the client and server systems may be intercepted by an attacker, who could then access sensitive information, such as credentials or data transmitted during the remote procedure calls.
3. Man-in-the-middle attacks: An attacker may intercept and modify the communication between the client and server, potentially altering the data or injecting malicious code into the transmitted messages.
4. Replay attacks: An attacker may intercept and record a valid remote procedure call, then replay it at a later time to gain unauthorized access or disrupt the application’s operations.
5. Denial of service (DoS) attacks: An attacker may flood the server with a large number of remote procedure calls, causing it to become overwhelmed and unresponsive, thereby disrupting the application’s operations.

To address these security concerns, developers should consider implementing the following security measures:

1. Authentication: Implement proper authentication mechanisms to verify the identities of the client and server systems, ensuring that only authorized users can access the remote procedures.
2. Authorization: Establish access controls to define which remote procedures specific users or systems can invoke, preventing unauthorized access to sensitive functionality.
3. Encryption: Encrypt the communication between the client and server systems using secure protocols, such as SSL/TLS, to protect sensitive data and prevent eavesdropping.
4. Message integrity: Use digital signatures or message authentication codes (MACs) to verify the integrity of the messages exchanged between the client and server systems, ensuring that they have not been tampered with during transmission.
5. Timestamps and nonces: Include timestamps and nonces in the messages to prevent replay attacks. Nonces are unique, random values that can be used only once, while timestamps help ensure the message’s freshness, preventing the reuse of intercepted messages.
6. Rate limiting and monitoring: Implement rate limiting to control the number of remote procedure calls accepted from a single source within a specific time frame, mitigating the risk of denial of service attacks. Additionally, monitor the system for unusual activity or patterns that may indicate an attack.

By incorporating these security measures, developers can minimize the risks associated with RPC-based communication and ensure that their distributed applications remain secure and reliable.

Attack Examples Using RPC

There have been several notable incidents in the past that leveraged RPC vulnerabilities or used the RPC protocol to propagate and compromise systems. Here are two such examples:

1. MSBlast (Blaster) Worm : The MSBlast worm, also known as Blaster or Lovesan, was a computer worm that spread rapidly in August 2003. It exploited a vulnerability in the DCOM (Distributed Component Object Model) interface of the Microsoft Windows RPC service. The vulnerability, identified as CVE-2003-0352 (also known as MS03-026), allowed remote attackers to execute arbitrary code via a crafted RPC request.

Once a system was infected, the worm would scan for other vulnerable systems on the local network and across the internet. MSBlast caused considerable disruption and downtime, affecting millions of computers and causing significant financial damage.

In response to this attack, Microsoft released a security patch (MS03-039) to address the vulnerability, and organizations were urged to apply the patch, update their antivirus software, and block certain ports used by the worm to propagate.

1. Conficker Worm : The Conficker worm, also known as Downadup or Kido, targeted a yet another vulnerability in the Microsoft Windows Server service, specifically in the RPC handling. The vulnerability, identified as CVE-2008-4250 (also known as MS08-067), allowed remote attackers to execute arbitrary code via a crafted RPC request.

The worm propagated by exploiting this vulnerability and by infecting USB drives and network shares. Conficker infected millions of computers worldwide, causing significant disruption to both businesses and government organizations.

Microsoft released a security patch (MS08-067) to address the vulnerability, and various security organizations collaborated to develop strategies to mitigate the impact of the worm and prevent its further spread.

These examples highlight the importance of securing RPC communication and applying patches and updates promptly to mitigate vulnerabilities and minimize the risk of large-scale attacks.

WireX Systems NDR can Help with RPC Investigations

WireX Systems Ne2ition NDR (Network Detection and Response) is a security solution that focuses on monitoring, detecting, and responding to threats and suspicious activities within the network. Ne2ition NDR leverages advanced technologies like machine learning, artificial intelligence, and deep packet inspection to analyze network traffic and identify potential threats in real-time.

Here’s how Ne2ition NDR can help with investigations of attacks over RPC (Remote Procedure Call):

1. Traffic monitoring and analysis: Ne2ition NDR solutions continuously monitor network traffic, including RPC communication between client and server systems. By analyzing this traffic, Ne2ition can identify suspicious or malicious activities, such as unauthorized remote procedure calls, which may indicate an attack.
2. Anomaly detection:Ne2ition NDR solution use machine learning and artificial intelligence to establish baseline patterns of normal network behavior. By comparing real-time network traffic against these baselines, Ne2ition NDR can detect anomalous activities that may be indicative of an attack, such as unusual RPC communication patterns or unexpected data transfers.
3. Deep packet inspection: Ne2ition NDR employs deep packet inspection to examine the contents of network packets, including RPC messages. This allows them to identify potentially malicious payloads, command and control (C2) communication, or attempts to exploit vulnerabilities in the RPC implementation.
4. Alerting and prioritization: Ne2ition solutions generate alerts for detected threats and suspicious activities, allowing security teams to prioritize their response and investigation efforts. By providing context and actionable intelligence, Ne2ition helps security teams focus on the most critical incidents and respond effectively.
5. Incident response and forensics: Ne2ition NDR tools can provide valuable insights for incident responders by capturing and storing network traffic data, including RPC communication. This data can be used to reconstruct the sequence of events during an attack, identify affected systems, and determine the scope of the breach, enabling effective containment, eradication, and recovery efforts.
6. Threat hunting and investigation: Ne2ition solutions can aid security analysts in proactive threat hunting by providing visibility into network activities and facilitating the investigation of potential threats. By examining RPC communication and other network data, analysts can uncover hidden threats, identify patterns of compromise, and develop proactive defenses.
7. Integration with other security solutions: Ne2ition NDR tools can be integrated with other security solutions, such as endpoint detection and response (EDR), security information and event management (SIEM), and threat intelligence platforms, to provide a comprehensive and coordinated defense against attacks over RPC and other vectors.

In summary, WireX Systems Ne2ition NDR can play a crucial role in investigating attacks over RPC by providing continuous monitoring, advanced threat detection, and valuable insights for incident response and threat hunting efforts. By leveraging WireX Systems Ne2ition solutions, security teams can enhance their visibility into network activities, respond to threats more effectively, and strengthen their overall security posture.

Overall, WireX Systems leverages the power of network analysis to detect and protect against cyber threats.

WireX Systems Ne2ition analyzes RPC traffic, extracts and indexes dozens of different attributes including the ones displays below to provide in-depth visibility and context for detection, response, forensics and hunting scenarios over RPC

These attributes will also help WireX Systems map into the MITRE ATT&CK framework techniques and tactics.

MITRE ATT&CK and RPC

The MITRE ATT&CK framework is a comprehensive knowledge base that describes various tactics and techniques used by adversaries during cyber attacks. While the framework does not specifically map attacks over RPC (Remote Procedure Call) to a single technique or tactic, several techniques related to RPC abuse can be mapped to MITRE ATT&CK tactics and techniques.

Here are a few relevant MITRE ATT&CK techniques that could involve RPC-based attacks:

1. T1077: Windows Admin Shares (Resource Development) Attackers may use RPC to establish connections to Windows admin shares for lateral movement or data exfiltration. They might attempt to access default network shares (C$, ADMIN$, or IPC$) to gain unauthorized access to resources or execute code remotely.
2. T1021: Remote Services (Lateral Movement) One of the sub-techniques, T1021.002 (SMB/Windows Admin Shares), mentions the use of DCE/RPC, which is used by the Server Message Block (SMB) protocol for communication. Attackers may use RPC to remotely execute code or move laterally within a network.
3. T1569: System Services (Execution) In this technique, adversaries may abuse system services to execute malicious payloads or establish persistence. Some sub-techniques like T1569.002 (Service Execution) and T1569.003 (Distributed Component Object Model) involve the use of RPC in the process of executing or controlling services.
4. T1210: Exploitation of Remote Services (Initial Access) Attackers may exploit vulnerabilities in remote services, including those using RPC, to gain initial access to a target network or system. This technique emphasizes exploiting remote services to bypass access controls and obtain unauthorized access.

While these techniques are not exclusively focused on RPC-based attacks, they demonstrate how RPC can be abused during various stages of an attack. It is essential for security teams to understand and monitor the use of RPC in their environment and implement appropriate defenses to protect against potential abuse.

Conclusion

In conclusion, RPC (Remote Procedure Call) is a communication protocol that enables distributed applications to request services or functions from other systems over a network. It provides a seamless and convenient way to execute procedures remotely, simplifying the development process for distributed systems. The primary steps in the RPC process involve client-side and server-side stubs, parameter serialization and deserialization, network communication, and remote procedure execution.

Despite its numerous benefits, RPC has some limitations, such as latency and performance issues, network reliability concerns, and increased complexity in error handling. Furthermore, RPC introduces several security concerns, including unauthorized access, eavesdropping, man-in-the-middle attacks, replay attacks, and denial of service attacks. To mitigate these risks, developers should implement robust security measures like authentication, authorization, encryption, message integrity, timestamps, nonces, rate limiting, and monitoring.

In order to protect systems from potential attacks over RPC, security teams should stay informed about relevant tactics and techniques from the MITRE ATT&CK framework and leverage security solutions like Network Detection and Response (NDR) to monitor, detect, and respond to threats within their network.

Overall, RPC remains a popular choice for developing distributed applications, as its benefits often outweigh its drawbacks. By understanding its limitations and addressing security concerns, developers can create robust, secure, and efficient distributed systems that leverage the power of remote procedure calls.