CVE-2026-102870 — Microsoft.AspNetCore.Comp…
HIGHCVE-2026-102870 is a high-severity (CVSS 8.8) Code Injection vulnerability in Microsoft.AspNetCore.Components.WebAssembly.Server. A fix is available for Microsoft.AspNetCore.Components.WebAssembly.Server — see the affected versions and patch details below.
Microsoft Security Advisory CVE-2026-102870 - ASP.NET Core Remote Code Execution Vulnerability
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-102870.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-102870 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
Microsoft.AspNetCore.Components.WebAssembly.Server.NETMicrosoft.AspNetCore.Components.WebAssembly.ServerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in the Blazor WebAssembly debugger included in Microsoft.AspNetCore.Components.WebAssembly.Server. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.
The Blazor WebAssembly debug proxy evaluates debugger expressions by generating and compiling C# source. Certain values originating in the application being debugged, including ToString() results, descriptions, and class names, are embedded in that generated source without consistent escaping. An attacker-controlled value can escape the generated string literal and execute code on a developer's machine when the developer evaluates an expression during debugging.
Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/445
CVSS Details
- Version: 3.1
- Severity: High
- Score: 8.8
- Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - Weakness: CWE-94 (Improper Control of Generation of Code ('Code Injection'))
Affected Platforms
- Platforms: Windows, Linux, macOS
- Architectures: All
<a name="affected-packages"></a>Affected Packages
The vulnerability affects Microsoft .NET projects that use an affected package version listed below.
| Package name | Affected version | Patched version |
|---|---|---|
| Microsoft.AspNetCore.Components.WebAssembly.Server | >= 10.0.0, <= 10.0.12 | 10.0.13 |
| Microsoft.AspNetCore.Components.WebAssembly.Server | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2.26478.115 |
Advisory FAQ
<a name="how-affected"></a>How do I know if I am affected?
You are affected if you use a vulnerable version of Microsoft.AspNetCore.Components.WebAssembly.Server to debug a Blazor WebAssembly application and evaluate an expression involving attacker-controlled application data.
<a name="how-fix"></a>How do I fix the issue?
- Install the latest supported version of .NET.
- Update
Microsoft.AspNetCore.Components.WebAssembly.Serverto the patched version for the .NET release used by the application.
Once the updated package or runtime is installed, restart the debugger and development environment.
Other Information
Reporting Security Issues
If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.
Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.
Support
You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repositories are located at https://github.com/dotnet/runtime and https://github.com/dotnet/aspnetcore. The Announcements repository (https://github.com/dotnet/announcements) will contain this bulletin as an issue and will include a link to a discussion issue.
Disclaimer
The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
External Links
Acknowledgements
alittleston3
Revisions
V1.0 (10/13/2026): Advisory published.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Microsoft.AspNetCore.Components.WebAssembly.Server | ≥ 10.0.0&&< 10.0.13 | 10.0.13dotnet add package Microsoft.AspNetCore.Components.WebAssembly.Server --version 10.0.13 |
| .NETNuGet | Microsoft.AspNetCore.Components.WebAssembly.Server | ≥ 11.0.0-preview.1&&< 11.0.0-rc.2.26478.115 | 11.0.0-rc.2.26478.115dotnet add package Microsoft.AspNetCore.Components.WebAssembly.Server --version 11.0.0-rc.2.26478.115 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Microsoft.AspNetCore.Components.WebAssembly.Server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Microsoft.AspNetCore.Components.WebAssembly.Server to 10.0.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-102870 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
A code injection vulnerability was found in the Blazor WebAssembly debug proxy of ASP.NET Core, which is shipped in the dotnet10.0 packages in Red Hat Enterprise Linux 8, 9, and 10, Red Hat In-Vehicle OS, and Fedora. The debug proxy embeds attacker-controlled values, such as ToString() results, descriptions, and class…
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.Source: Red Hat security advisory for CVE-2026-102870 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | dotnet10.0-0:10.0.113-1.el10_2 | RHSA-2026:86195 |
| Red Hat Enterprise Linux 8 | dotnet10.0-0:10.0.113-1.el8_10 | RHSA-2026:86192 |
| Red Hat Enterprise Linux 9 | dotnet10.0-0:10.0.113-1.el9_8 | RHSA-2026:86193 |
Frequently Asked Questions
Is CVE-2026-102870 in your dependencies?
Find it across NuGet, including transitive dependencies.