Researchers have disclosed a new Windows privilege escalation technique known as PhantomRPC, prompting security experts to call for stronger monitoring and controls around Windows Remote Procedure Call (RPC) infrastructure.
The technique, published by researchers in April, exploits weaknesses in how Windows RPC handles server provenance and impersonation. According to researchers, the issue stems from architectural design choices rather than a discrete software flaw, meaning no patch is currently available and all supported Windows systems are potentially affected.
Security specialists said the disclosure highlights a longstanding challenge in Windows environments, where service accounts with impersonation privileges can become a pathway to SYSTEM-level access.
Architectural risk
"PhantomRPC is a meaningful finding because it sits at the architectural level of Windows, not in an isolated feature that can simply be switched off or patched. What makes it particularly relevant for organizations is the lateral movement risk.
Once an attacker has a foothold, a flaw in how Windows systems communicate internally can become a pathway across the broader environment and that kind of silent spread is exactly what makes unpatched vulnerabilities so costly over time. We've written about how the Dell zero-day campaign went undetected for over 400 days precisely because the initial entry point wasn't caught in time.
Architectural changes are genuinely complex, and caution is understandable. But as we've covered in looking at the Microsoft Word zero-day earlier this year, the window between disclosure and active exploitation tends to be short and organizations are left managing that risk largely on their own.
When remediation isn't immediately available, mitigation becomes the working strategy. That means network segmentation to limit unnecessary exposure, tightening access controls around privileged accounts, and increasing monitoring for anomalous behavior in affected systems. As we note in our coverage of vulnerability remediation vs. mitigation, a mitigated vulnerability is still present so the goal is to reduce the blast radius while staying alert to how the situation evolves," said Sameed Aijas Ahmed Khan, Secure.com.
The research focuses on abuse of RPC communications and impersonation mechanisms that can allow an attacker who already possesses specific privileges to elevate access further. Experts noted that while the technique requires SeImpersonatePrivilege, that privilege is commonly available to service accounts in enterprise environments.
Escalation path
"PhantomRPC can turn a lower-privileged service compromise into SYSTEM-level control. For an organization, that means a normal foothold can become full host compromise. From there, an attacker may be able to access sensitive credentials, tamper with security tooling, establish persistence, and use the machine as a staging point for lateral movement. The important point is that this is not just a single bad component. Kaspersky's research points to a broader weakness in how Windows RPC handles server provenance, which means new abuse paths may continue to appear as researchers and attackers find additional privileged RPC clients," said Jacob Krell, Senior Director, Secure AI Solutions and Cybersecurity, Suzu Labs.
Krell argued that treating SeImpersonatePrivilege as a limiting prerequisite understates the operational risk because attackers frequently obtain access to service contexts where impersonation rights are already available.
He said organisations should focus on reducing unnecessary impersonation privileges, reviewing service account permissions and increasing visibility into RPC activity. He also pointed to ETW-based monitoring and ensuring legitimate RPC endpoints are correctly registered as practical defensive measures.
Microsoft stance
The disclosure has also renewed debate around how security issues are assessed when they rely on privileges already present within the operating system.
Researchers reported the issue to Microsoft in September 2025. Microsoft assessed it as moderate severity and did not issue a CVE or security update.
"Microsoft's decision not to patch is technically defensible under their traditional servicing criteria - since the attacker already needs SeImpersonatePrivilege - but it is operationally negligent in a landscape where attackers frequently use compromised service accounts as a beachhead. This "Moderate" rating ignores how easily these prerequisites are met during real-world lateral movement. Since no patch is forthcoming, defenders must treat this as a permanent architectural debt. To be clear, it is not so much that Microsoft decided not to patch, but at this time it appears that it cannot be patched without fundamentally changing how RPC functions," said Damon Small, Board Member, Xcape.
Defensive focus
Small said organisations should minimise the number of accounts granted SeImpersonatePrivilege and deploy monitoring controls capable of identifying unauthorised processes attempting to bind to known RPC ports.
"Because of the fundamental, architectural, nature of this vulnerability, we should expect to see variants on this attack pattern emerge in the future. Defenders should keep an eye on service accounts exhibiting anomalous behavior, such as spawning arbitrary listeners. This publication at this time is indicative of a pattern where Microsoft has downplayed an external researcher's finding because resolving the underlying issue is a deep architectural change. It is a bold strategy for Microsoft to claim a flaw is not a bug simply because you have to be halfway into the house before you can use it to unlock the safe," said Small.