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CVE-2026-96230 high CVSS 8.8

Cross-Site Scripting (XSS) in Microsoft.AspNetCore.Components.WebAssembly.Server (CVE-2026-96230)

Summary

Cross-site scripting in Microsoft.AspNetCore.Components.WebAssembly.Server (CVE-2026-96230). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 9.0.21 or later.

Original description

The description as published by the source.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability 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 development-server debug page can reflect unencoded exception text, allowing cross-origin script injection through the unauthenticated /_framework/debug endpoint used by dotnet watch.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/478

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-79 (Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'))

Affected Platforms

  • Platforms: Windows, Linux, macOS
  • Architectures: All

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.…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-96230 has been found in Microsoft.AspNetCore.Components.WebAssembly.Server.
Successful exploitation can lead to full system takeover. CVSS score: 8.8/10.
What to do: upgrade Microsoft.AspNetCore.Components.WebAssembly.Server to 9.0.21 or later.
If unsure, ask your IT team or search "Microsoft.AspNetCore.Components.WebAssembly.Server CVE-2026-96230" on the vendor's site.

CVE-2026-96230 (Microsoft.AspNetCore.Components.WebAssembly.Server) — CWE-79 / CVSS v3 8.8
Attack vector: remote (network-reachable) / unauthenticated
Patched: 9.0.21 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in Microsoft.AspNetCore.Components.WebAssembly.Server.

📍 Affected scope

Check the vendor advisory for the affected versions of Microsoft.AspNetCore.Components.WebAssembly.Server.

🔥 Severity

Severity: High (CVSS 8.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 9.0.21.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Microsoft.AspNetCore.Components.WebAssembly.Server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'Microsoft.AspNetCore.Components.WebAssembly.Server' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Microsoft.AspNetCore.Components.WebAssembly.Server を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade Microsoft.AspNetCore.Components.WebAssembly.Server to 9.0.21

    ステージング環境で 9.0.21 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

nuget Microsoft.AspNetCore.Components.WebAssembly.Server
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"9.0.21"}]}]

References

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