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High, CVSS 8.8amended

Microsoft Security Advisory CVE-2026-102870 - ASP.NET Core Remote Code Execution Vulnerability

CVE-2026-102870GHSA-g27p-qf6j-c96c

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (microsoft.aspnetcore.components.webassembly.server 11.0.0-rc.3.26522.148, 10.0.14), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-102870: 0.91% estimated exploitation activity in the next 30 days; percentile 59.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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 -…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 5 · amended ·

    Amended from osv record GHSA-g27p-qf6j-c96c

  2. Revision 4 · amended ·

    Amended from ghsa record GHSA-g27p-qf6j-c96c

  3. Revision 3 · amended ·

    Amended from ghsa record GHSA-g27p-qf6j-c96c

  4. Revision 2 · amended ·

    Amended from ghsa record GHSA-g27p-qf6j-c96c

  5. Revision 1 · created ·

    Published from osv record GHSA-g27p-qf6j-c96c

Agent brief

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# Patch Next advisory brief: CVE-2026-102870

Advisory: Microsoft Security Advisory CVE-2026-102870 - ASP.NET Core Remote Code Execution Vulnerability
IDs: CVE-2026-102870, GHSA-g27p-qf6j-c96c
Record: https://patchnext.com/advisories/cve-2026-102870 (revision 5, source checked 4 Nov 2026, 06:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.aspnetcore.components.webassembly.server 11.0.0-rc.3.26522.148, 10.0.14. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.components.webassembly.server: affected >= 10.0.0, < 10.0.14; >= 11.0.0-preview.1, < 11.0.0-rc.3.26522.148; fixed in 11.0.0-rc.3.26522.148, 10.0.14

## Suggested inspection (read-only)
- NuGet microsoft.aspnetcore.components.webassembly.server: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on microsoft.aspnetcore.components.webassembly.server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-g27p-qf6j-c96c (OSV record GHSA-g27p-qf6j-c96c lists affected ranges: NuGet microsoft.aspnetcore.components.webassembly.server >=10.0.0 =11.0.0-preview.1 <11.0.0-rc.2.26478.115 (fixed))
- Verified: https://github.com/advisories/GHSA-g27p-qf6j-c96c (GitHub-reviewed advisory GHSA-g27p-qf6j-c96c lists affected ranges: NuGet microsoft.aspnetcore.components.webassembly.server >=10.0.0 =11.0.0-preview.1 <=11.0.0-rc.1)
- Verified: https://github.com/advisories/GHSA-g27p-qf6j-c96c (GitHub-reviewed advisory GHSA-g27p-qf6j-c96c lists affected ranges: NuGet microsoft.aspnetcore.components.webassembly.server >=10.0.0 =11.0.0-preview.1 <11.0.0-rc.3.26522.148)
- Verified: https://osv.dev/vulnerability/GHSA-g27p-qf6j-c96c (OSV record GHSA-g27p-qf6j-c96c lists affected ranges: NuGet microsoft.aspnetcore.components.webassembly.server >=10.0.0 =11.0.0-preview.1 <11.0.0-rc.3.26522.148 (fixed))

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