CVE-2022-21911: Microsoft .NET Framework DOS Vulnerability

CVE-2022-21911 Overview

CVE-2022-21911 is a Denial of Service vulnerability affecting Microsoft .NET Framework across multiple versions and Windows operating systems. This vulnerability allows remote attackers to cause a denial of service condition in applications built on the .NET Framework without requiring any user interaction or authentication. The attack can be initiated over the network, making it particularly concerning for internet-facing applications and services relying on vulnerable .NET Framework versions.

Critical Impact

Remote attackers can cause service disruption by exploiting this .NET Framework vulnerability, potentially affecting availability of critical business applications and services without authentication.

Affected Products

• Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, and 4.8
• Microsoft Windows 7, 8.1, 10, 11 (various builds and architectures)
• Microsoft Windows Server 2008, 2008 R2, 2012, 2012 R2, 2016, 2019, 2022, and 20H2

Discovery Timeline

• January 11, 2022 - CVE-2022-21911 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-21911

Vulnerability Analysis

This Denial of Service vulnerability exists within the Microsoft .NET Framework, enabling remote attackers to disrupt the availability of applications and services built on the framework. The vulnerability can be exploited over the network without requiring any prior authentication or user interaction, which significantly increases the risk for exposed systems.

The widespread impact of this vulnerability stems from the extensive use of .NET Framework across enterprise environments. Applications running on affected versions may become unresponsive or crash when targeted by exploitation attempts, leading to service outages that can affect business operations.

Root Cause

While Microsoft has not disclosed specific technical details about the root cause (categorized as NVD-CWE-noinfo), Denial of Service vulnerabilities in .NET Framework typically arise from improper handling of specially crafted input data, resource exhaustion conditions, or algorithmic complexity issues that can be triggered remotely. The vulnerability likely involves a condition where malicious network requests can cause excessive resource consumption or trigger an unhandled exception state.

Attack Vector

The attack vector for CVE-2022-21911 is network-based, meaning an attacker can exploit this vulnerability remotely without any local access to the target system. The exploitation does not require authentication or user interaction, making it straightforward for attackers to target vulnerable systems. An attacker would typically send specially crafted requests to an application or service running on the affected .NET Framework version to trigger the denial of service condition.

The vulnerability affects the availability component of the system exclusively, with no impact on confidentiality or integrity. This indicates the attack results in service disruption rather than data exfiltration or modification.

Detection Methods for CVE-2022-21911

Indicators of Compromise

• Unexpected application crashes or hangs in .NET Framework-based applications
• Elevated CPU or memory consumption without corresponding legitimate workload increase
• Repeated service restarts or application pool recycling events in IIS hosting .NET applications
• Anomalous network traffic patterns targeting .NET services or endpoints

Detection Strategies

• Monitor Windows Event Logs for .NET Runtime errors, application crashes, and CLR exceptions
• Deploy network intrusion detection rules to identify potentially malicious traffic patterns targeting .NET applications
• Implement application performance monitoring (APM) to detect unusual resource consumption or response time degradation
• Review IIS logs and application logs for suspicious request patterns that correlate with service disruptions

Monitoring Recommendations

• Configure alerting for .NET Framework application crashes and unhandled exceptions in System Center or equivalent monitoring solutions
• Enable detailed logging on web applications and services to capture request details during incident analysis
• Monitor system resource utilization (CPU, memory, handle counts) for .NET processes to detect exploitation attempts
• Implement availability monitoring with automated alerting for critical .NET-based services

How to Mitigate CVE-2022-21911

Immediate Actions Required

• Apply Microsoft security updates from the January 2022 Patch Tuesday release immediately to all affected systems
• Prioritize patching for internet-facing applications and critical business services running on vulnerable .NET Framework versions
• Inventory all systems running affected .NET Framework versions across your environment
• Implement network segmentation to limit exposure of vulnerable systems while patching is in progress

Patch Information

Microsoft addressed this vulnerability in the January 2022 security updates. Organizations should apply the appropriate cumulative updates for their specific .NET Framework versions and Windows operating system combinations. For detailed patch information and download links, refer to the Microsoft Security Update Guide for CVE-2022-21911 and the Microsoft Security Advisory.

Workarounds

• Implement rate limiting and request throttling on application endpoints to mitigate potential DoS attempts
• Deploy web application firewalls (WAF) to filter potentially malicious traffic targeting .NET applications
• Consider temporarily taking non-critical vulnerable applications offline until patches can be applied
• Enable .NET Framework auto-updates through Windows Update to ensure timely patching of future vulnerabilities

# Verify installed .NET Framework versions on Windows
reg query "HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP" /s | findstr "Version"

# Check for pending Windows Updates related to .NET Framework
wmic qfe list brief /format:table | findstr "KB"