The RPC (Remote Procedure Call) Endpoint Mapper is a critical component in Windows networking that facilitates communication between clients and RPC services. It listens on TCP port 135 and maps RPC service identifiers to their corresponding network endpoints, enabling clients to locate and connect to the appropriate services.
What Is RPC Endpoint Mapping?
When an RPC service starts, it registers with the Endpoint Mapper, providing a unique identifier (UUID) and the dynamic port it's listening on. Clients querying the Endpoint Mapper receive this information to establish connections with the desired services. This mechanism supports dynamic port assignments, allowing services to operate without fixed port configurations.
Why Is It a Security Risk?
While essential for network operations, the RPC Endpoint Mapper can introduce several security vulnerabilities:
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Service Enumeration by Attackers
Attackers can exploit the Endpoint Mapper to enumerate available RPC services on a target system. Tools like rpcdump or Metasploit's dcerpc modules can retrieve a list of registered services, their UUIDs, and associated ports. This information aids attackers in identifying potential targets and vulnerabilities within the system.
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Anonymous Access Leading to Information Disclosure
By default, the Endpoint Mapper allows unauthenticated queries. This means that even without valid credentials, an attacker can gather details about the services running on a system, potentially exposing sensitive information and increasing the attack surface.
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Exploitation of Vulnerabilities
Certain vulnerabilities within the Endpoint Mapper can be exploited for malicious purposes. For instance, CVE-2025-26679 describes a "use-after-free" vulnerability in the RPC Endpoint Mapper Service, which could allow an attacker with local access to elevate privileges on the system.
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Facilitation of Lateral Movement
Once attackers identify accessible services via the Endpoint Mapper, they can exploit known vulnerabilities in those services to move laterally within a network, compromising additional systems and escalating their access.
Mitigation Strategies
To reduce the risks associated with the RPC Endpoint Mapper:
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Restrict Access: Implement firewall rules to limit access to TCP port 135, allowing only trusted hosts to communicate with the Endpoint Mapper.
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Enforce Authentication: Configure the Endpoint Mapper to require authentication for service queries, preventing anonymous enumeration.
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Regularly Update Systems: Ensure that all systems are up-to-date with the latest security patches to mitigate known vulnerabilities.
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Monitor Network Traffic: Use intrusion detection systems (IDS) and regular network monitoring to detect unusual activities related to RPC communications.
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Limit Exposed Services: Disable unnecessary RPC services and ensure that only essential services are registered with the Endpoint Mapper.
While the RPC Endpoint Mapper is integral to Windows networking, it poses significant security risks if not properly secured. By understanding its functions and potential vulnerabilities, organizations can implement appropriate safeguards to protect their systems from exploitation.
