High7.5

Microsoft Security Advisory CVE-2026-42899 – ASP.NET Core Denial of Service Vulnerability

CVE-2026-42899 GHSA-9v76-4qcc-frgh

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (microsoft.aspnetcore.app.runtime.linux-arm64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-musl-arm64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.osx-x64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-arm 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.win-x86 10.0.8, 9.0.16, 8.0.27; 7 more packages under Affected packages), 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.

Add to your agent

Affected packages

NuGet microsoft.aspnetcore.app.runtime.linux-arm64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.osx-x64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.linux-arm
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.win-x86
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.linux-x64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.win-arm
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64
Affected
>= 8.0.0, <= 8.0.26>= 10.0.0, <= 10.0.7>= 9.0.0, <= 9.0.15
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.osx-arm64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.win-x64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27
NuGet microsoft.aspnetcore.app.runtime.win-arm64
Affected
>= 8.0.0, <= 8.0.26>= 9.0.0, <= 9.0.15>= 10.0.0, <= 10.0.7
Fixed in
9.0.16, 10.0.8, 8.0.27

Sources

GitHub Advisory Database and maintainer security advisories on GitHub
GitHub-reviewed advisory GHSA-9v76-4qcc-frgh lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.win-arm >=8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 <=10.0.7; NuGet…
VerifiedObserved 26 Oct 2026, 17:04 UTCStructured GitHub Advisory Database record (type=reviewed) from the GitHub REST API.

Severity and exploitation

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

EPSS

CVE-2026-42899: 2.43% estimated exploitation activity in the next 30 days; percentile 84.26 (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 .NET 8.0, .NET 9.0, and .NET 10.0. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. Loop with unreachable exit condition ('infinite loop') in ASP.NET Core allows an unauthorized attacker to deny service over a network. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/397 CVSS Details - Version: 3.1 - Severity: - Score: 7.5 - Vector: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C - Weakness: CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') Affected Platforms - Platforms: All - Architectures: All <a name="affected-packages"</aAffected Packages The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below <a name=".NET 10"</a.NET 10 Package name | Affected version | Patched version…

Dates and revisions

Published by the source: 18 May 2026, 19:10 UTC
Last modified by the source: 18 May 2026, 19:11 UTC
Source last checked: 26 Oct 2026, 17:04 UTC

Revision 1 · created · 26 Oct 2026
Published from ghsa record GHSA-9v76-4qcc-frgh

Agent brief

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# Patch Next advisory brief: CVE-2026-42899

Advisory: Microsoft Security Advisory CVE-2026-42899 – ASP.NET Core Denial of Service Vulnerability
IDs: CVE-2026-42899, GHSA-9v76-4qcc-frgh
Record: https://patchnext.com/advisories/cve-2026-42899 (revision 1, source checked 26 Oct 2026, 17:04 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 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-musl-arm64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.osx-x64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-arm 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.win-x86 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-x64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-musl-arm 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.win-arm 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.linux-musl-x64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.osx-arm64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.win-x64 10.0.8, 9.0.16, 8.0.27; microsoft.aspnetcore.app.runtime.win-arm64 10.0.8, 9.0.16, 8.0.27. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.aspnetcore.app.runtime.linux-arm64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.osx-x64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.linux-arm: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.win-x86: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.linux-x64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-arm: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.win-arm: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.linux-musl-x64: affected >= 8.0.0, <= 8.0.26; >= 10.0.0, <= 10.0.7; >= 9.0.0, <= 9.0.15; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.osx-arm64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.win-x64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27
- NuGet microsoft.aspnetcore.app.runtime.win-arm64: affected >= 8.0.0, <= 8.0.26; >= 9.0.0, <= 9.0.15; >= 10.0.0, <= 10.0.7; fixed in 9.0.16, 10.0.8, 8.0.27

## 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.win-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.win-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-9v76-4qcc-frgh (GitHub-reviewed advisory GHSA-9v76-4qcc-frgh lists affected ranges: NuGet microsoft.aspnetcore.app.runtime.win-arm >=8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 =8.0.0 =9.0.0 =10.0.0 <=10.0.7; NuGet…)

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