.NET 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

EPSS

• CVE-2026-26127: 2.13% estimated exploitation activity in the next 30 days; percentile 81.99 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Microsoft Security Advisory CVE-2026-26127 – .NET Denial of Service Vulnerability Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in .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. A denial of service vulnerability exists in .NET and Microsoft.Bcl.Memory due to an out-of-bounds read when decoding malformed Base64Url input. Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/384 CVSS Details - Version: 3.1 - Score: 7.5 - 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 - Severity: High - Weakness: CWE-129 (Improper Validation of Array Index); CWE-125 (Out-of-bounds Read) Affected Platforms - Platforms: All - Architectures: All Affected Products <a name=".NET 9"</a.NET 9 Package name | Affected version | Patched version ------------ | ---------------- |…

Published by the source

11 Mar 2026, 21:11 UTC

Last modified by the source

12 Mar 2026, 20:32 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-73j8-2gch-69rq

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# Patch Next advisory brief: CVE-2026-26127

Advisory: .NET Denial of Service Vulnerability
IDs: CVE-2026-26127, GHSA-73j8-2gch-69rq
Record: https://patchnext.com/advisories/cve-2026-26127 (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.netcore.app.runtime.win-x86 10.0.4, 9.0.14; microsoft.netcore.app.runtime.win-arm64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-musl-x64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-arm64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-arm 10.0.4, 9.0.14; microsoft.netcore.app.runtime.osx-x64 10.0.4, 9.0.14; microsoft.bcl.memory 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-x64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.osx-arm64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-musl-arm 10.0.4, 9.0.14; microsoft.netcore.app.runtime.win-arm 10.0.4, 9.0.14; microsoft.netcore.app.runtime.linux-musl-arm64 10.0.4, 9.0.14; microsoft.netcore.app.runtime.win-x64 10.0.4, 9.0.14. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet microsoft.netcore.app.runtime.win-x86: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.win-arm64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-arm64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-arm: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.osx-x64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.bcl.memory: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-x64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.osx-arm64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.win-arm: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14
- NuGet microsoft.netcore.app.runtime.win-x64: affected >= 9.0.0, <= 9.0.13; >= 10.0.0, <= 10.0.3; fixed in 10.0.4, 9.0.14

## Suggested inspection (read-only)
- NuGet microsoft.netcore.app.runtime.win-x86: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.osx-x64: check the installed version with your package manager.
- NuGet microsoft.bcl.memory: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-x64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.osx-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-arm: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.linux-musl-arm64: check the installed version with your package manager.
- NuGet microsoft.netcore.app.runtime.win-x64: 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.netcore.app.runtime.win-x86, microsoft.netcore.app.runtime.win-arm64, microsoft.netcore.app.runtime.linux-musl-x64, microsoft.netcore.app.runtime.linux-arm64, microsoft.netcore.app.runtime.linux-arm, microsoft.netcore.app.runtime.osx-x64, microsoft.bcl.memory, microsoft.netcore.app.runtime.linux-x64, microsoft.netcore.app.runtime.osx-arm64, microsoft.netcore.app.runtime.linux-musl-arm, microsoft.netcore.app.runtime.win-arm, microsoft.netcore.app.runtime.linux-musl-arm64, microsoft.netcore.app.runtime.win-x64.
- 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-73j8-2gch-69rq (GitHub-reviewed advisory GHSA-73j8-2gch-69rq lists affected ranges: NuGet microsoft.bcl.memory >=9.0.0 =10.0.0 =9.0.0 =10.0.0 =9.0.0 =10.0.0 =9.0.0 =10.0.0 =9.0.0 =10.0.0 <=10.0.3; NuGet…)

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