CVE-2026-25173: Windows RRAS RCE Vulnerability

CVE-2026-25173 Overview

CVE-2026-25173 is an integer overflow vulnerability affecting the Windows Routing and Remote Access Service (RRAS). This flaw allows an authorized attacker to execute arbitrary code over a network by exploiting improper handling of integer arithmetic operations within the RRAS component. The vulnerability is classified under CWE-122 (Heap-based Buffer Overflow), indicating that the integer overflow condition leads to memory corruption that can be leveraged for code execution.

Critical Impact

An authorized attacker can achieve remote code execution over the network, potentially compromising affected Windows systems running RRAS and gaining full control of the target environment.

Affected Products

• Windows Routing and Remote Access Service (RRAS)
• Windows Server systems with RRAS role enabled
• Windows systems utilizing remote access functionality

Discovery Timeline

• 2026-03-10 - CVE-2026-25173 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2026-25173

Vulnerability Analysis

This vulnerability stems from an integer overflow or wraparound condition in the Windows Routing and Remote Access Service (RRAS). When processing network requests, the RRAS component performs integer arithmetic operations that can overflow when handling specially crafted input. The overflow condition causes the calculated buffer size to wrap around to a smaller value than expected, leading to a heap-based buffer overflow (CWE-122) when data is subsequently written to the undersized buffer.

The attack requires network access and low privileges, but does require user interaction to successfully exploit. Once exploited, an attacker can achieve high impact to confidentiality, integrity, and availability of the target system. This could result in complete system compromise, allowing the attacker to execute arbitrary code in the context of the RRAS service.

Root Cause

The root cause is improper validation of integer values used in buffer size calculations within the RRAS component. When certain network operations involve arithmetic on user-influenced values, the code fails to check for integer overflow conditions before allocating memory buffers. This results in allocation of a buffer smaller than required, and subsequent write operations exceed the buffer boundaries, corrupting heap memory.

Attack Vector

The attack is conducted over the network (AV:N) and requires low complexity to execute. An attacker with valid low-level privileges on the target system can send specially crafted network requests to the RRAS service. These requests contain values designed to trigger the integer overflow during buffer size calculations. User interaction is required to complete the attack chain.

Upon successful exploitation, the attacker gains code execution capabilities on the target system. The exploitation flow typically involves:

1. Establishing a network connection to the RRAS service
2. Sending malformed requests containing values that trigger integer overflow
3. Overwriting heap metadata or adjacent memory structures
4. Redirecting execution flow to attacker-controlled code

The vulnerability mechanism involves integer arithmetic that can wrap around due to insufficient bounds checking. When the RRAS service processes incoming network data, it calculates required buffer sizes using values from the request. If these calculations overflow, a smaller-than-needed buffer is allocated, and subsequent data copy operations corrupt adjacent heap memory. For detailed technical information, refer to the Microsoft CVE-2026-25173 Advisory.

Detection Methods for CVE-2026-25173

Indicators of Compromise

• Unexpected RRAS service crashes or restarts indicating potential exploitation attempts
• Anomalous network traffic patterns to RRAS service ports
• Memory access violations in rasman.dll or related RRAS components logged in Windows Event logs
• Suspicious process spawning from RRAS service context

Detection Strategies

• Monitor Windows Event Logs for RRAS service errors, crashes, or unexpected terminations
• Implement network intrusion detection rules for malformed RRAS protocol traffic
• Deploy endpoint detection and response (EDR) solutions to identify heap corruption exploitation patterns
• Enable crash dump collection for RRAS components to analyze potential exploitation attempts

Monitoring Recommendations

• Enable advanced auditing for Windows Routing and Remote Access Service events
• Monitor for unusual network connections originating from RRAS service processes
• Implement alerting for RRAS service instability or repeated restart patterns
• Review Windows Security logs for privilege escalation following RRAS activity

How to Mitigate CVE-2026-25173

Immediate Actions Required

• Apply Microsoft security updates addressing CVE-2026-25173 as soon as available
• Disable Windows Routing and Remote Access Service on systems where it is not required
• Implement network segmentation to restrict access to RRAS services from untrusted networks
• Review and restrict user accounts with access to RRAS functionality

Patch Information

Microsoft has released a security advisory for this vulnerability. Organizations should apply the official security update from Microsoft to fully remediate this issue. Consult the Microsoft CVE-2026-25173 Advisory for specific patch details and download links.

Workarounds

• Disable RRAS service if not required: Set-Service RemoteAccess -StartupType Disabled
• Implement firewall rules to restrict network access to RRAS service ports
• Use Windows Firewall with Advanced Security to limit RRAS connections to trusted IP ranges only
• Consider VPN alternatives that do not rely on RRAS functionality

# Disable RRAS service on Windows systems (PowerShell)
Stop-Service RemoteAccess -Force
Set-Service RemoteAccess -StartupType Disabled

# Verify service is disabled
Get-Service RemoteAccess | Select-Object Name, Status, StartType