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CVE-2026-70159 high CVSS 7.5

Vulnerability in Microsoft.AspNetCore.SignalR.Common (CVE-2026-70159)

Summary

Vulnerability in Microsoft.AspNetCore.SignalR.Common (CVE-2026-70159). Risk of unauthorized operations or information disclosure. Exploitable via MessageBuffer.ResendAsync. 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.SignalR.Common and Microsoft.AspNetCore.SignalR.Core. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

SignalR stateful reconnect clients can indefinitely block broadcasts through MessageBuffer.ResendAsync backpressure and retain associated resources.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/452

CVSS Details

  • Version: 3.1

  • Severity: High

  • Score: 7.5

  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

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.SignalR.Common >= 10.0.0, <= 10.0.12 10.0.13
Microsoft.AspNetCore.SignalR.Core >= 1.0.0, <= 1.2.13 1.2.14
Microsoft.AspNetCore.SignalR.Common >= 11.0.0-pre…

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-2026-70159 has been found in Microsoft.AspNetCore.SignalR.Common.
Attackers can target a specific entry point like MessageBuffer.ResendAsync over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade Microsoft.AspNetCore.SignalR.Common to 9.0.21 or later.
If unsure, ask your IT team or search "Microsoft.AspNetCore.SignalR.Common CVE-2026-70159" on the vendor's site.

CVE-2026-70159 (Microsoft.AspNetCore.SignalR.Common) — CWE-770 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: MessageBuffer.ResendAsync
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

A vulnerability (CWE-770) exists in Microsoft.AspNetCore.SignalR.Common. Attackers reach the vulnerable code path via MessageBuffer.ResendAsync without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of Microsoft.AspNetCore.SignalR.Common. Attack surface: MessageBuffer.ResendAsync.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 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.SignalR.Common' . 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.SignalR.Common' . | 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.SignalR.Common 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.SignalR.Common 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.SignalR.Common
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"9.0.21"}]}]
nuget Microsoft.AspNetCore.SignalR.Core
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.2.14"}]}]

References

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