CVE-2021-26423 Overview
CVE-2021-26423 is a Denial of Service vulnerability affecting .NET Core and Visual Studio. This vulnerability allows remote attackers to cause a denial of service condition in affected Microsoft products without requiring authentication or user interaction. The vulnerability exists in the way .NET Core and Visual Studio handle certain network requests, potentially allowing an attacker to exhaust system resources and render the application unresponsive.
Critical Impact
This network-accessible vulnerability can be exploited remotely without authentication to cause service disruption across .NET Core applications, Visual Studio environments, and PowerShell Core installations.
Affected Products
- Microsoft .NET
- Microsoft .NET Core
- Microsoft PowerShell Core
- Microsoft Visual Studio 2017
- Microsoft Visual Studio 2019 (including version 8.10 for macOS)
Discovery Timeline
- August 12, 2021 - CVE-2021-26423 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2021-26423
Vulnerability Analysis
This vulnerability is classified as a Denial of Service (DoS) flaw that can be triggered remotely over the network. The attack requires no privileges and no user interaction, making it particularly dangerous in production environments. When exploited, the vulnerability causes high impact to system availability while not affecting confidentiality or integrity of the system.
The vulnerability affects multiple Microsoft development tools and runtime environments, including .NET, .NET Core, PowerShell Core, and Visual Studio 2017/2019. Organizations running web applications or services built on these platforms are potentially at risk of service disruption.
Root Cause
The root cause of CVE-2021-26423 lies in improper handling of network requests within the .NET Core runtime. While Microsoft has not disclosed specific technical details about the vulnerable code paths, the vulnerability allows attackers to send specially crafted requests that consume excessive system resources, leading to denial of service conditions. The CWE classification indicates no specific weakness information has been publicly disclosed (NVD-CWE-noinfo).
Attack Vector
The attack vector for this vulnerability is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by sending malicious network requests to a vulnerable .NET Core application or service. The attack complexity is low, meaning no special conditions or circumstances need to be met for successful exploitation.
The vulnerability can be exploited against any network-exposed application built on the affected .NET Core runtime versions. Once triggered, the denial of service condition prevents legitimate users from accessing the affected service until it is restarted or the attack subsides.
Detection Methods for CVE-2021-26423
Indicators of Compromise
- Unusual spikes in network traffic targeting .NET Core applications or services
- Unexpected application crashes or unresponsiveness in .NET-based services
- Elevated CPU or memory consumption in dotnet processes without corresponding legitimate workload
- Service restart events in Windows Event Log or application logs for affected services
Detection Strategies
- Monitor .NET Core application performance metrics for anomalous resource consumption patterns
- Implement network intrusion detection rules to identify potential DoS attack patterns targeting .NET services
- Configure application health checks to detect service degradation or unresponsiveness
- Review system logs for process termination events related to .NET Core or Visual Studio processes
Monitoring Recommendations
- Deploy application performance monitoring (APM) solutions to track .NET application health in real-time
- Set up alerts for abnormal resource utilization in environments running affected Microsoft products
- Implement rate limiting and request throttling on externally-exposed .NET Core web applications
- Monitor network traffic patterns for potential DoS attack signatures
How to Mitigate CVE-2021-26423
Immediate Actions Required
- Apply the security patches provided by Microsoft for all affected products immediately
- Inventory all systems running .NET Core, .NET, PowerShell Core, and Visual Studio 2017/2019
- Prioritize patching externally-accessible services and applications built on affected frameworks
- Consider implementing network-level protections such as rate limiting while patches are being deployed
Patch Information
Microsoft has released security updates to address this vulnerability. Organizations should apply the appropriate patches based on their installed products. Detailed patch information and download links are available in the Microsoft Security Advisory for CVE-2021-26423.
For .NET Core applications, update to the latest patched version of the runtime. Visual Studio users should apply the latest security updates through the Visual Studio Installer. PowerShell Core users should update to the latest patched release.
Workarounds
- Implement network segmentation to limit exposure of vulnerable applications to untrusted networks
- Deploy a web application firewall (WAF) or reverse proxy to filter potentially malicious requests
- Enable rate limiting on load balancers or application gateways to mitigate DoS attack impact
- Configure application restart policies to automatically recover from denial of service conditions
- Monitor and set resource limits for .NET processes to prevent complete system resource exhaustion
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
