Microsoft Security Advisory CVE-2026-109478 - ASP.NET Core Denial of Service Vulnerability

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core. This advisory provides guidance on updating affected applications and components. Processing comma-separated HTTP header values can cause excessive allocations and resource exhaustion.

Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/515

CVSS Details - Version: 3.1 - Severity: High - Score: 7.5 (base score) - Vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C` - Weakness: CWE-407

Affected Platforms - Platforms: Windows, Linux, macOS - Architectures: All

Affected Packages The tables list affected version ranges and fixed package versions. Runtime and standalone deliveries are listed separately.

.NET 8.0 - affected runtime packages Package | Affected version | Patched version --- | --- | ---…

Published by the source

11 Nov 2026, 00:22 UTC

Last modified by the source

11 Nov 2026, 00:30 UTC

Source last checked

11 Nov 2026, 07:45 UTC

1. Revision 2 · amended · 11 Nov 2026

   Amended from osv record GHSA-r3qf-p3jm-8h4p

2. Revision 1 · created · 11 Nov 2026

   Published from ghsa record GHSA-r3qf-p3jm-8h4p

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# Patch Next advisory brief: CVE-2026-109478

Advisory: Microsoft Security Advisory CVE-2026-109478 - ASP.NET Core Denial of Service Vulnerability
IDs: CVE-2026-109478, GHSA-r3qf-p3jm-8h4p
Record: https://patchnext.com/advisories/cve-2026-109478 (revision 2, source checked 11 Nov 2026, 07:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: microsoft.aspnetcore.app.runtime.linux-arm64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.linux-musl-arm64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.osx-x64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.linux-arm 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.win-x86 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.linux-x64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.linux-musl-arm 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.linux-musl-x64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.osx-arm64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.win-x64 9.0.0-preview.4.24267.6, 8.0.34; microsoft.aspnetcore.app.runtime.win-arm64 9.0.0-preview.4.24267.6, 8.0.34. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.win-x86: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.win-x64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: affected >= 8.0.0-preview.1.23112.2, < 8.0.34; >= 9.0.0-preview.1.24081.5, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.2.24128.4, < 9.0.0-preview.4.24267.6; >= 9.0.0-preview.3.24172.13, < 9.0.0-preview.4.24267.6; fixed in 9.0.0-preview.4.24267.6, 8.0.34

## Suggested inspection (read-only)
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-x64: check the installed version with your package manager.
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: 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.app.runtime.linux-arm64, microsoft.aspnetcore.app.runtime.linux-musl-arm64, microsoft.aspnetcore.app.runtime.osx-x64, microsoft.aspnetcore.app.runtime.linux-arm, microsoft.aspnetcore.app.runtime.win-x86, microsoft.aspnetcore.app.runtime.linux-x64, microsoft.aspnetcore.app.runtime.linux-musl-arm, microsoft.aspnetcore.app.runtime.linux-musl-x64, microsoft.aspnetcore.app.runtime.osx-arm64, microsoft.aspnetcore.app.runtime.win-x64, microsoft.aspnetcore.app.runtime.win-arm64.
- 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://github.com/advisories/GHSA-r3qf-p3jm-8h4p (GitHub-reviewed advisory GHSA-r3qf-p3jm-8h4p lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.linux-arm >=8.0.0-preview.1.23112.2 =9.0.0-preview.1.24081.5 =9.0.0-preview.2.24128.4 =9.0.0-preview.3.24172.13 =8.0.0-preview.1.23112.2 =9.0.0-preview.1.24081.5 =9.0.0-preview.2.24128.4…)
- Verified: https://osv.dev/vulnerability/GHSA-r3qf-p3jm-8h4p (OSV record GHSA-r3qf-p3jm-8h4p lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.linux-arm >=8.0.0-preview.1.23112.2 =9.0.0-preview.1.24081.5 =9.0.0-preview.2.24128.4 =9.0.0-preview.3.24172.13 =8.0.0-preview.1.23112.2 =9.0.0-preview.1.24081.5 <9.0.0-preview.4.24267.6 (fixed),…)

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