CVE-2021-24112: Microsoft .NET Core RCE Vulnerability

CVE-2021-24112 Overview

CVE-2021-24112 is a critical remote code execution vulnerability affecting Microsoft .NET Core and related products. This vulnerability allows attackers to execute arbitrary code on vulnerable systems through network-based attack vectors without requiring user interaction or prior authentication. The flaw impacts multiple Microsoft development frameworks including .NET, .NET Core, Mono, and Visual Studio 2019.

Critical Impact

Successful exploitation of this vulnerability enables remote attackers to execute arbitrary code with the privileges of the affected application, potentially leading to complete system compromise, data theft, or further lateral movement within the network.

Affected Products

• Microsoft .NET
• Microsoft .NET Core
• Microsoft Mono
• Microsoft Visual Studio 2019 for macOS

Discovery Timeline

• 2021-02-25 - CVE-2021-24112 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-24112

Vulnerability Analysis

This remote code execution vulnerability exists within the .NET Core framework and affects how the runtime processes certain operations. The flaw allows an unauthenticated attacker to leverage network access to trigger arbitrary code execution on target systems running vulnerable versions of the affected Microsoft products.

The vulnerability is particularly severe because it can be exploited remotely without requiring any privileges or user interaction. An attacker who successfully exploits this vulnerability could gain complete control over the affected system, potentially accessing sensitive data, installing malicious software, or using the compromised system as a pivot point for further attacks.

Root Cause

The specific root cause of CVE-2021-24112 is classified as "NVD-CWE-noinfo" in the National Vulnerability Database, indicating that detailed weakness enumeration information has not been publicly disclosed. Microsoft has addressed this vulnerability through security updates, though the specific vulnerable code path or component has not been publicly detailed.

Attack Vector

The attack vector for CVE-2021-24112 is network-based, allowing remote exploitation. An attacker can target vulnerable .NET Core applications accessible over the network without requiring authentication credentials or user interaction. The exploitation does not require any special conditions, making it feasible for attackers to target publicly accessible applications.

The vulnerability can be exploited by sending specially crafted requests to vulnerable .NET Core applications. Once triggered, the attacker gains the ability to execute arbitrary code within the context of the affected application, potentially leading to full system compromise.

Detection Methods for CVE-2021-24112

Indicators of Compromise

• Unexpected process spawning from .NET Core application processes
• Anomalous network connections originating from web application servers
• Unusual file system activity in .NET runtime directories
• Suspicious PowerShell or command prompt executions from web application contexts

Detection Strategies

• Monitor .NET Core application logs for unusual error patterns or exceptions
• Implement network intrusion detection rules to identify exploitation attempts
• Deploy endpoint detection and response (EDR) solutions to monitor .NET process behavior
• Review application-level logging for unexpected input patterns or malformed requests

Monitoring Recommendations

• Enable verbose logging for all .NET Core applications exposed to untrusted networks
• Implement file integrity monitoring on critical .NET runtime directories
• Configure alerts for unusual child process creation from .NET application processes
• Monitor outbound network connections from application servers for potential command and control traffic

How to Mitigate CVE-2021-24112

Immediate Actions Required

• Apply Microsoft security updates for all affected .NET, .NET Core, Mono, and Visual Studio 2019 installations immediately
• Inventory all systems running affected Microsoft products to ensure complete coverage
• Prioritize patching for internet-facing applications and servers
• Consider temporarily taking vulnerable applications offline if patching cannot be performed immediately

Patch Information

Microsoft has released security updates to address CVE-2021-24112. Detailed patch information and security guidance are available through the Microsoft Security Response Center Advisory. Organizations should apply the appropriate updates for their installed versions of .NET, .NET Core, Mono, and Visual Studio 2019 for macOS.

Workarounds

• Implement network segmentation to limit exposure of vulnerable applications
• Deploy Web Application Firewalls (WAF) with rules to filter malicious requests
• Restrict network access to vulnerable applications using firewall rules
• Monitor affected systems closely until patches can be applied

# Verify .NET Core version to determine if patching is required
dotnet --list-sdks
dotnet --list-runtimes

# Update .NET Core SDK and runtime to latest patched version
# For Windows (using winget)
winget upgrade Microsoft.DotNet.SDK.6

# For Linux (Ubuntu/Debian)
sudo apt-get update && sudo apt-get upgrade dotnet-sdk-6.0