CVE-2026-57108: Microsoft .NET Core DoS Vulnerability

CVE-2026-57108 Overview

CVE-2026-57108 is a type confusion vulnerability in Microsoft .NET Core that allows an unauthenticated remote attacker to trigger a denial of service condition over the network. The flaw is classified under CWE-843, which covers access of a resource using an incompatible type. The vulnerability affects .NET runtime deployments across Windows, macOS, and Linux platforms, making it a cross-platform risk for any service exposing .NET-based network endpoints. Microsoft published the advisory on July 14, 2026, and the issue is tracked in the Microsoft Security Update Guide.

Critical Impact
An unauthenticated network attacker can crash or hang .NET Core services, disrupting availability of production applications without requiring privileges or user interaction.

Affected Products

Microsoft .NET Core (multiple versions) on Windows
Microsoft .NET Core on Apple macOS
Microsoft .NET Core on Linux distributions

Discovery Timeline

2026-07-14 - CVE-2026-57108 published to NVD
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-57108

Vulnerability Analysis

CVE-2026-57108 is a type confusion flaw (CWE-843) in the .NET Core runtime. Type confusion occurs when code allocates or references a resource as one type but later accesses it as a different, incompatible type. The mismatched interpretation causes the runtime to operate on memory it does not correctly understand, leading to invalid state transitions.

In this case, the miscast object triggers an unrecoverable exception or runtime abort in the affected .NET process. Because the vulnerability is reachable across the network without authentication, an attacker can repeatedly send crafted input to force the target service to crash. The impact is limited to availability, with no confidentiality or integrity compromise reported by Microsoft.

The EPSS probability at the time of publication was 1.099% (62nd percentile), and there is no evidence of public exploitation or listing in the CISA Known Exploited Vulnerabilities catalog.

Root Cause

The root cause lies in the runtime's handling of certain typed objects during deserialization or network message processing. When the runtime accesses these objects under an incompatible type assumption, internal safety checks fail and the process terminates. Microsoft has not published low-level implementation details beyond the advisory reference.

Attack Vector

Exploitation requires only network access to a service built on the affected .NET Core runtime. The attacker sends malformed data that traverses the vulnerable code path. No credentials, tokens, or user interaction are required. The result is a repeated denial of service against any exposed .NET application, including web APIs, gRPC services, and background workers listening on network sockets.

No public proof-of-concept code has been released. See the Microsoft CVE-2026-57108 Update Guide for vendor technical details.

Detection Methods for CVE-2026-57108

Indicators of Compromise

Unexpected crashes or restarts of dotnet host processes on servers exposing network endpoints
Windows Event Log entries showing .NET Runtime errors with exception types tied to invalid casts or type mismatches
Repeated System.InvalidCastException or fatal runtime aborts appearing in application logs
Bursts of malformed traffic targeting .NET service ports immediately preceding process failures

Detection Strategies

Monitor process lifetime metrics for dotnet.exe and dotnet binaries and alert on abnormal termination rates
Correlate application crash telemetry with inbound network events from the same source IP within short time windows
Inspect crash dumps for stack frames referencing type resolution or deserialization code paths in the .NET runtime

Monitoring Recommendations

Enable Windows Error Reporting and centralize .NET Runtime event IDs 1023 and 1026 to SIEM for correlation
Track HTTP 5xx spikes and TCP reset counts on services fronted by .NET applications
Baseline normal restart frequency for containerized .NET workloads in Kubernetes and alert on abnormal restart loops

How to Mitigate CVE-2026-57108

Immediate Actions Required

Apply the .NET Core security updates referenced in the Microsoft CVE-2026-57108 Update Guide to all affected runtimes on Windows, macOS, and Linux
Inventory every host and container image that ships a vulnerable .NET Core runtime version and prioritize internet-facing workloads
Restart .NET services after patching to ensure the updated runtime is loaded

Patch Information

Microsoft has released security updates addressing CVE-2026-57108 through the standard .NET update channels. Administrators should install the latest .NET Core runtime and SDK versions distributed through Microsoft Update, apt, yum, dnf, brew, or container base image refreshes. Container images based on mcr.microsoft.com/dotnet/* should be rebuilt against updated tags.

Workarounds

Restrict inbound access to .NET Core services using network segmentation and firewall rules where patching is delayed
Place a validating reverse proxy or Web Application Firewall in front of exposed .NET endpoints to reject malformed payloads
Configure process supervisors such as systemd, IIS, or Kubernetes to automatically restart crashed .NET workers to reduce downtime while patches are staged

bash

# Update the .NET runtime on common platforms after applying vendor patches
# Ubuntu / Debian
sudo apt-get update && sudo apt-get install --only-upgrade dotnet-runtime-8.0 aspnetcore-runtime-8.0

# RHEL / CentOS / Fedora
sudo dnf upgrade dotnet-runtime-8.0 aspnetcore-runtime-8.0

# macOS
brew upgrade --cask dotnet

# Verify installed runtime versions
dotnet --list-runtimes