CVE-2023-21708: Windows 10 1507 RCE Vulnerability

CVE-2023-21708 Overview

CVE-2023-21708 is a Remote Code Execution (RCE) vulnerability affecting the Remote Procedure Call (RPC) Runtime in Microsoft Windows operating systems. This vulnerability allows an unauthenticated remote attacker to execute arbitrary code on vulnerable systems by sending specially crafted RPC requests to the target system. The RPC Runtime is a fundamental Windows component that enables distributed computing and inter-process communication across networks.

Critical Impact

Successful exploitation enables unauthenticated remote attackers to execute arbitrary code with SYSTEM privileges, potentially leading to complete system compromise across enterprise Windows environments.

Affected Products

• Microsoft Windows 10 (versions 1507, 1607, 1809, 20H2, 21H2, 22H2)
• Microsoft Windows 11 (versions 21H2, 22H2)
• Microsoft Windows Server 2008 (SP2, R2 SP1)
• Microsoft Windows Server 2012 (including R2)
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 2022

Discovery Timeline

• March 14, 2023 - CVE-2023-21708 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-21708

Vulnerability Analysis

This vulnerability exists within the Windows Remote Procedure Call (RPC) Runtime, specifically related to an Integer Underflow condition (CWE-191). The RPC Runtime is responsible for handling remote procedure calls that allow programs to request services from other programs located on different computers in a network. When processing maliciously crafted RPC requests, the runtime fails to properly validate certain integer values, leading to an underflow condition that can be leveraged for code execution.

The vulnerability requires no user interaction and can be exploited remotely over the network without authentication. An attacker who successfully exploits this vulnerability could execute code in the context of the RPC service, which typically runs with elevated SYSTEM privileges. This makes the vulnerability particularly dangerous in enterprise environments where Windows systems are networked together.

Root Cause

The root cause of CVE-2023-21708 is an Integer Underflow vulnerability (CWE-191) in the RPC Runtime component. Integer underflows occur when an arithmetic operation results in a value that is smaller than the minimum value the data type can represent, causing the value to wrap around to a very large number. In the context of the RPC Runtime, this underflow condition leads to improper memory allocation or buffer operations, which can then be exploited to achieve arbitrary code execution.

Attack Vector

The attack vector is network-based and does not require any user interaction or authentication. An attacker can exploit this vulnerability by:

1. Identifying vulnerable Windows systems with RPC services accessible over the network
2. Crafting malicious RPC requests designed to trigger the integer underflow condition
3. Sending the malicious requests to the target system's RPC endpoint (typically TCP port 135 or dynamic RPC ports)
4. Leveraging the resulting memory corruption to execute arbitrary code with SYSTEM privileges

The vulnerability mechanism involves improper integer handling in the RPC Runtime when processing specific request parameters. When the underflow occurs, subsequent memory operations may use an incorrect buffer size, leading to out-of-bounds memory access that attackers can manipulate for code execution. For detailed technical information, refer to the Microsoft Security Advisory.

Detection Methods for CVE-2023-21708

Indicators of Compromise

• Unusual network traffic patterns targeting TCP port 135 or dynamic RPC ports from external sources
• Unexpected process creation under svchost.exe hosting RPC services
• Memory access violations or crashes in rpcrt4.dll logged in Windows Event Logs
• Anomalous outbound connections initiated by RPC-related processes

Detection Strategies

• Monitor network traffic for suspicious RPC communications, particularly malformed or oversized RPC requests
• Deploy network intrusion detection signatures targeting RPC protocol anomalies
• Enable advanced audit policies for RPC connection events in Windows Security Event logs
• Utilize endpoint detection tools to monitor for suspicious behavior in RPC Runtime processes

Monitoring Recommendations

• Configure SentinelOne Singularity to alert on suspicious RPC-related activities and process injection attempts
• Implement network segmentation monitoring to detect lateral movement attempts via RPC
• Review Windows Security Event Log entries for Event ID 5712 (RPC connection failures) and correlated events
• Establish baseline RPC traffic patterns to identify deviations indicative of exploitation attempts

How to Mitigate CVE-2023-21708

Immediate Actions Required

• Apply the Microsoft security updates released in the March 2023 Patch Tuesday immediately
• Restrict access to RPC services from untrusted networks using Windows Firewall or network-level controls
• Implement network segmentation to limit exposure of Windows RPC services to only necessary systems
• Enable SentinelOne Singularity real-time protection to detect and block exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability as part of the March 2023 security updates. Organizations should apply the appropriate patches for their Windows versions immediately. Detailed patch information and download links are available in the Microsoft Security Update Guide for CVE-2023-21708.

Workarounds

• Block inbound traffic on TCP port 135 and dynamic RPC ports at the network perimeter for untrusted networks
• Disable RPC services on systems where they are not required for business operations
• Implement host-based firewall rules to restrict RPC access to authorized IP addresses only
• Consider using IPsec policies to authenticate and encrypt RPC traffic between trusted systems

# Windows Firewall rule to block inbound RPC from untrusted networks
netsh advfirewall firewall add rule name="Block Inbound RPC Port 135" dir=in action=block protocol=tcp localport=135 profile=public

# Restrict RPC access to specific IP ranges (adjust IP range as needed)
netsh advfirewall firewall add rule name="Allow RPC from Trusted Network" dir=in action=allow protocol=tcp localport=135 remoteip=10.0.0.0/8,192.168.0.0/16