CVE-2020-1597: ASP.NET Core Denial of Service Vulnerability

CVE-2020-1597 Overview

A denial of service vulnerability exists when ASP.NET Core improperly handles web requests. An attacker who successfully exploited this vulnerability could cause a denial of service against an ASP.NET Core web application. The vulnerability can be exploited remotely, without authentication.

A remote unauthenticated attacker could exploit this vulnerability by issuing specially crafted requests to the ASP.NET Core application. The update addresses the vulnerability by correcting how the ASP.NET Core web application handles web requests.

Critical Impact

Unauthenticated remote attackers can render ASP.NET Core web applications unavailable by sending specially crafted HTTP requests, potentially causing significant business disruption without requiring any credentials or prior access.

Affected Products

• Microsoft ASP.NET Core 2.1
• Microsoft ASP.NET Core 3.1
• Microsoft Visual Studio 2017
• Microsoft Visual Studio 2019
• Fedora 32 and 33

Discovery Timeline

• 2020-08-17 - CVE-2020-1597 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2020-1597

Vulnerability Analysis

This denial of service vulnerability stems from improper handling of web requests within the ASP.NET Core framework. The flaw allows unauthenticated remote attackers to craft malicious HTTP requests that cause the web application to consume excessive resources or crash entirely.

The vulnerability affects the core request processing pipeline in ASP.NET Core, making it particularly dangerous as it impacts any application built on the affected framework versions. Since no authentication is required to exploit this vulnerability, any ASP.NET Core application exposed to the network is potentially at risk.

Root Cause

The root cause lies in improper input handling within the ASP.NET Core request processing mechanism. The framework fails to properly validate or limit certain aspects of incoming web requests, allowing attackers to trigger resource exhaustion or application failure through malformed or specially constructed HTTP requests.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target ASP.NET Core web application accessible over the network
2. Crafting specially formatted HTTP requests designed to trigger the vulnerable code path
3. Sending these malicious requests to the target application
4. The application improperly processes the requests, leading to denial of service

The vulnerability manifests in the web request handling components of ASP.NET Core. Attackers can send specially crafted requests that exploit the improper handling logic, causing resource exhaustion or application crashes. See the Microsoft Security Advisory CVE-2020-1597 for complete technical details.

Detection Methods for CVE-2020-1597

Indicators of Compromise

• Unusual patterns of HTTP requests with malformed or oversized headers
• Sudden spikes in memory or CPU utilization on ASP.NET Core application servers
• Application pool crashes or restarts occurring without scheduled maintenance
• Increased error rates in IIS or Kestrel logs related to request processing

Detection Strategies

• Monitor web server logs for unusual request patterns or high volumes of requests from single sources
• Implement application performance monitoring (APM) to detect abnormal resource consumption
• Configure alerts for ASP.NET Core application crashes or unexpected restarts
• Use web application firewalls (WAF) to identify and block malformed HTTP requests

Monitoring Recommendations

• Enable detailed logging for ASP.NET Core applications to capture request processing anomalies
• Set up real-time monitoring dashboards for application health metrics including response times and error rates
• Configure network traffic analysis to identify potential DoS attack patterns
• Implement SentinelOne's application visibility capabilities to detect exploitation attempts

How to Mitigate CVE-2020-1597

Immediate Actions Required

• Apply the latest security updates from Microsoft for ASP.NET Core 2.1 and 3.1
• Update Visual Studio 2017 and 2019 installations to the latest patched versions
• For Fedora systems, apply the updated packages referenced in the Fedora security announcements
• Implement rate limiting and request size restrictions as an additional defense layer

Patch Information

Microsoft has released security updates to address this vulnerability by correcting how ASP.NET Core web applications handle web requests. Organizations should apply the appropriate patches based on their installed versions:

• For ASP.NET Core 2.1 and 3.1: Update to the latest patched runtime versions available from Microsoft
• For Visual Studio 2017/2019: Install the latest cumulative updates that include the security fix

Detailed patch information is available in the Microsoft Security Advisory CVE-2020-1597. Fedora users should reference the Fedora Package Announcement for distribution-specific updates.

Workarounds

• Implement request throttling at the load balancer or reverse proxy level to limit request rates
• Configure web application firewalls to filter potentially malicious request patterns
• Deploy applications behind a content delivery network (CDN) with DDoS protection capabilities
• Temporarily restrict network access to affected applications to trusted IP ranges if immediate patching is not feasible

# Example: Configure request limits in Kestrel (Program.cs or appsettings.json)
# Add these settings to limit request body size and header count
# appsettings.json configuration:
# {
#   "Kestrel": {
#     "Limits": {
#       "MaxRequestBodySize": 30000000,
#       "MaxRequestHeaderCount": 100,
#       "MaxRequestHeadersTotalSize": 32768
#     }
#   }
# }