CVE-2026-105016: Microsoft Security Advisory CVE-2026-105016 - Microsoft QUIC Remote Code Execution Vulnerability

The flaw is a heap-based buffer overflow (CWE-122) in the Microsoft QUIC library that .NET uses for HTTP/3 on Windows. A crafted IPv6 QUIC packet that reaches the Microsoft QUIC HTTP/3 path triggers it. The attacker needs no credentials and no user interaction, and the CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:N with high confidentiality, integrity and availability impact (9.8).

In practice, a .NET service that listens for HTTP/3 over QUIC on Windows, such as a Kestrel server with HTTP/3 enabled, can be attacked by anyone who can send UDP packets to it over IPv6. A successful exploit means code execution in the service process, with the service account's access to its data, secrets and network.

The advisory says the vulnerable package version is exactly 2.5.11-ci.156755675 of Microsoft.Native.Quic.MsQuic.Schannel. It does not say whether exploitation has been seen in the wild, and it gives no proof of concept.

Windows only, all architectures. Microsoft says .NET 8.0, 9.0, 10.0 and 11 RC2 that use the NuGet package Microsoft.Native.Quic.MsQuic.Schannel at exactly 2.5.11-ci.156755675 are affected. Self-contained applications built against an impacted version are also vulnerable.

dotnet --info

This lists installed runtimes and SDKs. For your own projects, check the package reference:

dotnet list package --include-transitive

Install the latest servicing update for your supported .NET release. If you installed .NET SDKs through Visual Studio, update Visual Studio and it will update the SDKs. If your application references Microsoft.Native.Quic.MsQuic.Schannel directly, update the reference to 2.5.11-ci.159417053 or later.

Restart your applications after updating the runtime or SDK. Self-contained applications must be recompiled and redeployed. The advisory lists no workaround.

The advisory gives no log signature or indicator. Look for crashes or unexpected restarts of .NET services that serve HTTP/3 on Windows, and for unusual inbound UDP traffic over IPv6 to the QUIC port, typically 443. Check the Windows event log for application faults in the service process. Inventory your hosts for the vulnerable package version.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in Microsoft QUIC as used by .NET 8.0, .NET 9.0, .NET 10.0, and .NET 11 RC2 on Windows. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A crafted IPv6 QUIC packet can reach the Microsoft QUIC HTTP/3 path without authentication or user interaction and trigger remote code execution.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/446

CVSS Details

• Version: 3.1
• Severity: Critical
• Score: 9.8
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Weakness: CWE-122 (Heap-based Buffer Overflow)

Affected Platforms

• Platforms: Windows
• 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.Native.Quic.MsQuic.Schannel | >= 2.5.11-ci.156755675, <= 2.5.11-ci.156755675 | 2.5.11-ci.159417053

Advisory FAQ

How do I know if I am affected?

If your application uses a package version listed in [affected packages](#affected-packages), it is exposed to the vulnerability.

How do I fix the issue?

1. Install the latest servicing update for your supported .NET release. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs.
2. If your application directly references Microsoft.Native.Quic.MsQuic.Schannel, update the package reference to version 2.5.11-ci.159417053 or later. You can list the .NET versions installed on your system by running the dotnet --info command.

Once you have installed the updated runtime or SDK, restart your applications for the update to take effect.

Additionally, if you have deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.

Other Information

Reporting Security Issues

If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program, including terms and conditions, are at https://aka.ms/corebounty.

Support

You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repositories are located at https://github.com/dotnet/runtime. The Announcements repository (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

External Links

CVE-2026-105016

Acknowledgements

pwn2addr

Revisions

V1.0 (10/13/2026): Advisory published.