CVE-2026-102870: ASP.NET Core RCE Vulnerability

CVE-2026-102870 Overview

CVE-2026-102870 is a code injection vulnerability in ASP.NET Core that allows an unauthorized attacker to execute code over a network. The flaw is tracked under CWE-94: Improper Control of Generation of Code and affects the generation path used by ASP.NET Core components. Microsoft published guidance in the Microsoft Security Update CVE-2026-102870 advisory. Successful exploitation requires user interaction, but no authentication or special privileges are needed on the target. The vulnerability impacts confidentiality, integrity, and availability of the hosting process.

Critical Impact

Attackers can execute arbitrary code on ASP.NET Core hosts over the network when a user is induced to perform an action, enabling full compromise of the application process.

Affected Products

• ASP.NET Core (versions listed in the Microsoft advisory)
• Applications built on vulnerable ASP.NET Core runtime versions
• .NET hosting environments running impacted ASP.NET Core packages

Discovery Timeline

• 2026-10-13 - CVE-2026-102870 published to NVD
• 2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-102870

Vulnerability Analysis

The vulnerability stems from improper control over how ASP.NET Core generates code at runtime. Input that reaches a code generation path is not sufficiently constrained, allowing attacker-controlled content to be interpreted as executable code rather than data. When a victim interacts with a crafted request or resource, the resulting code is produced and executed in the context of the ASP.NET Core process. This yields remote code execution against the hosting application without prior authentication.

Because the attack vector is network-based and user interaction is required, exploitation typically relies on luring an authenticated user, administrator, or developer to a malicious endpoint or crafted payload. The EPSS probability is approximately 0.78%, indicating current exploitation likelihood is modest but non-trivial for an unauthenticated RCE in a widely deployed web framework.

Root Cause

The root cause is improper neutralization of input used during code generation in ASP.NET Core [CWE-94]. Trust boundaries between untrusted request data and the code generation routine are not enforced, allowing attacker input to influence the final generated code. Microsoft's advisory describes the affected component and patched behavior in the Microsoft Security Update CVE-2026-102870 advisory.

Attack Vector

An attacker delivers a crafted request, link, or resource that an application user interacts with. The ASP.NET Core runtime processes the input through the vulnerable code generation path and produces executable code reflecting the attacker's payload. The code then runs with the privileges of the ASP.NET Core worker process, enabling arbitrary command execution, data theft, or lateral movement.

No verified exploit code is available at the time of publication. Refer to the Microsoft advisory for component-level technical details.

Detection Methods for CVE-2026-102870

Indicators of Compromise

• Unexpected child processes spawned by ASP.NET Core worker processes such as dotnet.exe, w3wp.exe, or Microsoft.AspNetCore.* hosts.
• Outbound network connections from web application processes to unknown or recently registered domains.
• Anomalous file writes to web application directories, including new .dll, .cs, or .cshtml files created at runtime.
• Elevated error or compile-time log entries from Razor or runtime code generation components following inbound requests.

Detection Strategies

• Monitor ASP.NET Core hosts for process lineage anomalies where web worker processes launch shells, scripting engines, or cmd.exe.
• Inspect HTTP request logs for payloads containing code constructs, unusual escape sequences, or oversized parameters targeting endpoints that perform templating or dynamic rendering.
• Correlate authentication events with subsequent code generation or compilation activity to identify suspicious user-triggered sequences.

Monitoring Recommendations

• Enable detailed request logging and runtime diagnostics on ASP.NET Core applications in production.
• Forward web server, application, and host telemetry to a centralized analytics platform for cross-source correlation.
• Alert on new persistence artifacts under IIS or Kestrel application directories after inbound traffic.

How to Mitigate CVE-2026-102870

Immediate Actions Required

• Apply the ASP.NET Core security updates referenced in the Microsoft Security Update CVE-2026-102870 advisory to all affected hosts.
• Inventory applications using ASP.NET Core and prioritize internet-facing workloads for patching.
• Restrict administrative and developer access to production ASP.NET Core endpoints until patches are deployed.
• Review recent web server logs for suspicious requests targeting dynamic rendering or code generation endpoints.

Patch Information

Microsoft has released updates addressing CVE-2026-102870 through standard .NET and ASP.NET Core servicing channels. Review the Microsoft Security Update CVE-2026-102870 advisory for affected versions and the corresponding fixed releases, then upgrade the runtime and shared framework on all hosts.

Workarounds

• Place a web application firewall in front of ASP.NET Core applications and block requests containing suspicious code constructs.
• Disable or restrict endpoints that perform dynamic templating, Razor compilation, or runtime code generation where not required.
• Enforce least-privilege execution for the ASP.NET Core worker process to limit post-exploitation impact.
• Require authentication and strict input validation on any endpoint that influences code generation paths.

# Update .NET runtime and ASP.NET Core shared framework on Linux
sudo apt-get update
sudo apt-get install --only-upgrade dotnet-runtime-* aspnetcore-runtime-*

# Verify installed runtimes
dotnet --list-runtimes