Microsoft Security Advisory CVE-2026-58649 | .NET Information Disclosure Vulnerability

# Microsoft Security Advisory CVE-2026-58649 – .NET Information Disclosure Vulnerability

## Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET SDK dotnet watch. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

The dotnet watch BrowserRefreshServer does not adequately validate cross-origin WebSocket origins, potentially allowing IL and PDB information disclosure.

## Discussion

Discussion for this issue can be found at https://github.com/dotnet/sdk/issues/56166

## CVSS Details

- **Version:** 3.1
- **Severity:** Medium
- **Score:** 6.5
- **Vector:** `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N`
- **Weakness:** CWE-346 (Origin Validation Error)

## Affected Platforms

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

## Affected .NET SDKs
The vulnerability affects installations of the .NET SDK in the version ranges listed below. These are SDK versions, not NuGet package versions.

### .NET 11 RC1
SDK feature band | Affected SDK version | Patched SDK version
---------------- | -------------------- | -------------------
11.0.1xx RC1 | Earlier .NET 11 previews | 11.0.100-rc.1

### .NET 10
SDK feature band | Affected SDK version | Patched SDK version
---------------- | -------------------- | -------------------
10.0.1xx | >= 10.0.100, <= 10.0.110 | 10.0.111
10.0.3xx | >= 10.0.300, <= 10.0.399 | 10.0.400

### .NET 9
SDK feature band | Affected SDK version | Patched SDK version
---------------- | -------------------- | -------------------
9.0.1xx | >= 9.0.100, <= 9.0.119 | 9.0.120
9.0.3xx | >= 9.0.300, <= 9.0.316 | 9.0.317

### .NET 8
SDK feature band | Affected SDK version | Patched SDK version
---------------- | -------------------- | -------------------
8.0.1xx | >= 8.0.100, <= 8.0.129 | 8.0.130
8.0.4xx | >= 8.0.400, <= 8.0.423 | 8.0.424

## Advisory FAQ

### How do I know if I am affected?

If using an SDK listed in [affected .NET SDKs](#affected-sdks), you're exposed to the vulnerability.

### How do I fix the issue?

1. To fix the issue please install the latest version of .NET. 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. Update each affected SDK feature band to the patched version listed above. You can list the versions you have installed by running the `dotnet --info` command.

Once you have installed the updated SDK, restart dotnet watch and your applications for the update to take effect.

## 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](https://msrc.microsoft.com/report/vulnerability/new). Further information can be found in the MSRC [Report an Issue FAQ](https://www.microsoft.com/msrc/faqs-report-an-issue).

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 repos are located at https://github.com/dotnet/sdk. The Announcements repo (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-2026-58649](https://www.cve.org/CVERecord?id=CVE-2026-58649)

### Revisions

V1.0 (09/08/2026): Advisory published.

Start with the linked discussion at dotnet/sdk#56166 and review the affected and patched SDK ranges in this advisory. Use dotnet --info to inspect installed SDKs; no repository change or contributor-defined completion criteria are provided here.

Written by the indexing model from the issue text.