CVE-2026-62781: Windows 10 1607 Buffer Overflow Vulnerability

CVE-2026-62781 Overview

CVE-2026-62781 is a heap-based buffer overflow [CWE-122] in the Microsoft Windows Remote Procedure Call (RPC) Runtime. An unauthenticated attacker can send crafted RPC traffic across the network to trigger memory corruption and execute code in the context of the RPC service. The flaw affects a broad range of Windows client and server releases, from Windows 10 1607 through Windows 11 26H1 and Windows Server 2012 through Windows Server 2025. Microsoft published the advisory on 2026-08-11 and updated it on 2026-08-13. No public exploit or CISA KEV listing exists at the time of writing.

Critical Impact
Successful exploitation grants remote code execution across the network with no user interaction and no prior authentication, exposing every internet- and intranet-reachable Windows host.

Affected Products

Microsoft Windows 10 (1607, 1809, 21H2, 22H2) on x86, x64, and ARM64
Microsoft Windows 11 (23H2, 24H2, 25H2, 26H1) on x64 and ARM64
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-08-11 - CVE-2026-62781 published to NVD
2026-08-11 - Microsoft releases security update for CVE-2026-62781
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-62781

Vulnerability Analysis

The vulnerability resides in the Windows RPC Runtime, the shared library that marshals and dispatches RPC messages for user-mode and kernel-mode services. Attackers exploit the flaw by sending malformed RPC data over a network transport such as TCP/135, SMB named pipes, or other endpoints exposed by RPC-dependent services. The runtime allocates a heap buffer whose size is derived from attacker-controlled fields, then copies data past the allocated boundary. Successful memory corruption yields code execution in the address space of the vulnerable RPC endpoint, which frequently runs as NETWORK SERVICE or SYSTEM. Attack complexity is high because the attacker must win a race or align heap state to achieve reliable control of the corrupted allocation.

Root Cause

The defect is a classic heap-based buffer overflow [CWE-122]. RPC Runtime performs length validation that does not fully account for the size of embedded structures during unmarshalling, allowing the copy operation to overrun the destination chunk on the process heap.

Attack Vector

Exploitation is entirely network based and requires no credentials or user interaction. An attacker with reachability to any RPC endpoint on a vulnerable host can transmit a crafted request. Environments that expose RPC to untrusted networks or that permit lateral RPC traffic between workstations face the highest exposure.

No public proof-of-concept code has been released. See the Microsoft Security Update CVE-2026-62781 advisory for vendor technical details.

Detection Methods for CVE-2026-62781

Indicators of Compromise

Unexpected child processes spawned by svchost.exe hosting RPC services, particularly cmd.exe, powershell.exe, or rundll32.exe.
Crashes or repeated restarts of RpcSs, RpcEptMapper, or other RPC-dependent services logged in the System event log.
Anomalous inbound connections to TCP/135 or high dynamic RPC ports from untrusted network segments.

Detection Strategies

Hunt for post-exploitation behavior chained to RPC service processes, including credential dumping, lsass.exe access, and remote service creation.
Correlate Windows Error Reporting entries for RPC Runtime faults with concurrent inbound RPC connections from a single source.
Alert on new RPC endpoint bindings or unusual interface UUIDs observed on domain controllers and member servers.

Monitoring Recommendations

Enable Sysmon Event IDs 1, 3, and 11 with a ruleset that flags process creation and network activity originating from RPC service hosts.
Forward Windows Security, System, and Application logs plus network flow data to a centralized analytics platform for cross-host correlation.
Baseline expected RPC traffic between servers and workstations, then alert on deviations such as workstation-to-workstation RPC.

How to Mitigate CVE-2026-62781

Immediate Actions Required

Apply the Microsoft security update referenced in the MSRC advisory for CVE-2026-62781 to every affected Windows client and server.
Prioritize patching internet-exposed hosts, domain controllers, and jump servers that terminate RPC traffic from other segments.
Inventory RPC exposure using endpoint mapper queries and reduce attack surface on hosts that cannot be patched immediately.

Patch Information

Microsoft has released fixes through the standard Windows Update channel. Consult the Microsoft Security Update CVE-2026-62781 page for KB article numbers that map to each affected build.

Workarounds

Block inbound TCP/135 and the dynamic RPC port range (49152-65535 by default) at perimeter and internal firewalls where RPC is not required.
Restrict RPC endpoints to authenticated peers using IPsec or Windows Defender Firewall connection security rules.
Segment management networks so that only jump hosts can initiate RPC to sensitive servers such as domain controllers.

bash

# Windows Defender Firewall: block inbound RPC endpoint mapper from untrusted zones
New-NetFirewallRule -DisplayName "Block Inbound RPC EPM (CVE-2026-62781)" `
  -Direction Inbound -Protocol TCP -LocalPort 135 `
  -RemoteAddress Untrusted -Action Block -Profile Any