Cybersecurity researchers have introduced new findings associated to a now-patched safety difficulty in Microsoft’s Home windows Distant Process Name (RPC) communication protocol that may very well be abused by an attacker to conduct spoofing assaults and impersonate a recognized server.
The vulnerability, tracked as CVE-2025-49760 (CVSS rating: 3.5), has been described by the tech large as a Home windows Storage spoofing bug. It was mounted in July 2025 as a part of its month-to-month Patch Tuesday replace. Particulars of the safety defect had been shared by SafeBreach researcher Ron Ben Yizhak on the DEF CON 33 safety convention this week.
“Exterior management of file title or path in Home windows Storage permits a licensed attacker to carry out spoofing over a community,” the corporate stated in an advisory launched final month.
The Home windows RPC protocol makes use of universally distinctive identifiers (UUIDs) and an Endpoint Mapper (EPM) to allow using dynamic endpoints in client-server communications, and join an RPC shopper to an endpoint registered by a server.
The vulnerability basically makes it doable to control a core element of the RPC protocol and stage what’s known as an EPM poisoning assault that enables unprivileged customers to pose as a official, built-in service with the aim of coercing a protected course of to authenticate in opposition to an arbitrary server of an attacker’s selecting.
Provided that the functioning of EPM is analogous to that of the Area Identify System (DNS) – it maps an interface UUID to an endpoint, simply the DNS resolves a website to an IP handle – the assault performs out like DNS poisoning, through which a menace actor tampers with DNS knowledge to redirect customers to malicious web sites –
- Poison the EPM
- Masquerade as a official RPC Server
- Manipulate RPC shoppers
- Obtain native/area privilege escalation through an ESC8 assault
“I used to be shocked to find that nothing stopped me from registering recognized, built-in interfaces that belong to core providers,” Ben Yizhak stated in a report shared with The Hacker Information. “I anticipated, for instance, if Home windows Defender had a novel identifier, no different course of would have the ability to register it. However that was not the case.”
“Once I tried registering an interface of a service that was turned off, its shopper related to me as an alternative. This discovering was unbelievable—there have been no safety checks accomplished by the EPM. It related shoppers to an unknown course of that wasn’t even operating with admin privileges.”
The crux of the assault hinges on discovering interfaces that are not mapped to an endpoint, in addition to people who may very well be registered proper after the system boots by making the most of the truth that many providers are set to “delayed begin” for efficiency causes, and make the boot course of sooner.
In different phrases, any service with a guide startup is a safety danger, because the RPC interface would not be registered on boot, successfully making it inclined to a hijack by permitting an attacker to register an interface earlier than the unique service does.
SafeBreach has additionally launched a software known as RPC-Racer that can be utilized to flag insecure RPC providers (e.g., the Storage Service or StorSvc.dll) and manipulate a Protected Course of Mild (PPL) course of (e.g., the Supply Optimization service or DoSvc.dll) to authenticate the machine account in opposition to any server chosen by the attacker.
The PPL expertise ensures that the working system solely masses trusted providers and processes, and safeguards operating processes from termination or an infection by malicious code. It was launched by Microsoft with the discharge of Home windows 8.1.
At a excessive degree, the whole assault sequence is as follows –
- Create a scheduled activity that shall be executed when the present person logs in
- Register the interface of the Storage Service
- Set off the Supply Optimization service to ship an RPC request to the Storage Service, leading to it connecting to the attacker’s dynamic endpoint
- Name the strategy GetStorageDeviceInfo(), which causes the Supply Optimization service to obtain an SMB share to a rogue server arrange by the attacker
- The Supply Optimization service authenticates with the malicious SMB server with the machine account credentials, leaking the NTLM hash
- Stage an ESC8 assault to relay the coerced NTLM hashes to the web-based certificates enrollment providers (AD CS) and obtain privilege escalation
To perform this, an offensive open-source software like Certipy can be utilized to request a Kerberos Ticket-Granting Ticket (TGT) utilizing the certificates generated by passing the NTLM info to the AD CS server, after which leverage it to dump all secrets and techniques from the area controller.
SafeBreach stated the EPM poisoning approach may very well be additional expanded to conduct adversary-in-the-middle (AitM) and denial-of-service (DoS) assaults by forwarding the requests to the unique service or registering many interfaces and denying the requests, respectively. The cybersecurity firm additionally identified that there may very well be different shoppers and interfaces which might be possible susceptible to EPM poisoning.
To raised detect these sorts of assaults, safety merchandise can monitor calls to RpcEpRegister and use Occasion Tracing for Home windows (ETW), a safety function that logs occasions which might be raised by user-mode purposes and kernel-mode drivers.
“Identical to SSL pinning verifies that the certificates isn’t solely legitimate however makes use of a particular public key, the identification of an RPC server needs to be checked,” Ben Yizhak stated.
“The present design of the endpoint mapper (EPM) would not carry out this verification. With out this verification, shoppers will settle for knowledge from unknown sources. Trusting this knowledge blindly permits an attacker to manage the shopper’s actions and manipulate it to the attacker’s will.”
