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Vulnerabilities

Vulnerability · CVE-2026-66822

Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability

Published Oct 13, 2026 · catalog updated Oct 13, 2026 · Microsoft .NET 10.0

Check if you run it

No confirmed exploitation is on record for CVE-2026-66822. EPSS is 0.67%. Act only if a listed version of Microsoft .NET 10.0 is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium5.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.67%
Remediation
Version ranges on file
Affected products
NuGet Microsoft.NETCore.App.Runtime.linux-arm · NuGet Microsoft.NETCore.App.Runtime.linux-arm64 · NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm · NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm64 · NuGet Microsoft.NETCore.App.Runtime.linux-musl-x64 · NuGet Microsoft.NETCore.App.Runtime.linux-x64

## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Http. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. SocketsHttpHandler can retain a header across an HTTP redirect and leak basic proxy credentials to the destination server. ## Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/448 ## CVSS Details - **Version:** 3.1 - **Severity:** Moderate - **Score:** 5.9 - **Vector:** - **Weakness:** CWE-201 (Insertion of Sensitive Information Into Sent Data) ## Affected Platforms - **Platforms:** Windows, Linux, macOS - **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.NETCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm) | >= 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 9.0.0, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 11.0.0-preview.1, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 10.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, = 8.0.0, How do I know if I am affected? If using a package listed in [affected packages](#affected-packages), 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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • NuGet Microsoft.NETCore.App.Runtime.linux-arm11.0.0-preview.1 → 11.0.0-rc.2
  • NuGet Microsoft.NETCore.App.Runtime.linux-arm9.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.linux-arm649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm9.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.linux-musl-x649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.linux-x649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.osx-arm649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.osx-x649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.win-arm649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.win-x649.0.0 → 9.0.21
  • NuGet Microsoft.NETCore.App.Runtime.win-x869.0.0 → 9.0.21
  • nuget Microsoft.NETCore.App.Runtime.linux-arm>= 11.0.0-preview.1, <= 11.0.0-rc.1
  • nuget Microsoft.NETCore.App.Runtime.linux-arm>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.linux-arm64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.linux-musl-arm>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.linux-musl-arm64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.linux-musl-x64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.linux-x64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.osx-arm64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.osx-x64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.win-arm64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.win-x64>= 9.0.0, <= 9.0.20
  • nuget Microsoft.NETCore.App.Runtime.win-x86>= 9.0.0, <= 9.0.20
  • nuget microsoft.netcore.app.runtime.linux-armversion unspecified
  • nuget microsoft.netcore.app.runtime.linux-arm64version unspecified
  • nuget microsoft.netcore.app.runtime.linux-musl-armversion unspecified
  • nuget microsoft.netcore.app.runtime.linux-musl-arm64version unspecified
  • nuget microsoft.netcore.app.runtime.linux-musl-x64version unspecified
  • nuget microsoft.netcore.app.runtime.linux-x64version unspecified
  • nuget microsoft.netcore.app.runtime.osx-arm64version unspecified
  • nuget microsoft.netcore.app.runtime.osx-x64version unspecified
  • nuget microsoft.netcore.app.runtime.win-arm64version unspecified
  • nuget microsoft.netcore.app.runtime.win-x64version unspecified
  • nuget microsoft.netcore.app.runtime.win-x86version unspecified
  • vendor Microsoft .NET 10.0version unspecified

How to fix CVE-2026-66822

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-66822. EPSS is 0.67%. Act only if a listed version of Microsoft .NET 10.0 is installed.

Which versions are affected?

Compare what you have installed with Microsoft.NETCore.App.Runtime.linux-arm 11.0.0-preview.1 → 11.0.0-rc.2; Microsoft.NETCore.App.Runtime.linux-arm 9.0.0 → 9.0.21; Microsoft.NETCore.App.Runtime.linux-arm64 9.0.0 → 9.0.21; Microsoft.NETCore.App.Runtime.linux-musl-arm 9.0.0 → 9.0.21. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-201. EPSS 0.67%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 13, 2026 · Catalog

    Detected

    ## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Http. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. SocketsHttpHandler can retain a header across an HTTP redirect and leak basic proxy credentials to the destination server. ## Announcement Announc

  2. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-arm fixed in 9.0.21; Microsoft.NETCore.App.Runtime.linux-arm64 fixed in 9.0.21; Microsoft.NETCore.App.Runtime.linux-musl-arm fixed in 9.0.21; Microsoft.NETCore.App.Runtime.linux-musl-arm64 fixed in 9.0.21

  3. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-arm 9.0.0 → 9.0.21

  4. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-arm64 9.0.0 → 9.0.21

  5. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm 9.0.0 → 9.0.21

  6. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-musl-arm64 9.0.0 → 9.0.21

  7. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-musl-x64 9.0.0 → 9.0.21

  8. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-x64 9.0.0 → 9.0.21

  9. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.osx-arm64 9.0.0 → 9.0.21

  10. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.osx-x64 9.0.0 → 9.0.21

  11. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.win-arm64 9.0.0 → 9.0.21

  12. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.win-x64 9.0.0 → 9.0.21

  13. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.win-x86 9.0.0 → 9.0.21

  14. Oct 13, 2026 · Catalog

    Fix available

    NuGet Microsoft.NETCore.App.Runtime.linux-arm 11.0.0-preview.1 → 11.0.0-rc.2

  15. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-arm fixed in 9.0.21

  16. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-arm64 fixed in 9.0.21

  17. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-musl-arm fixed in 9.0.21

  18. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-musl-arm64 fixed in 9.0.21

  19. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-musl-x64 fixed in 9.0.21

  20. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-x64 fixed in 9.0.21

  21. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.osx-arm64 fixed in 9.0.21

  22. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.osx-x64 fixed in 9.0.21

  23. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.win-arm64 fixed in 9.0.21

  24. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.win-x64 fixed in 9.0.21

  25. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.win-x86 fixed in 9.0.21

  26. Oct 13, 2026 · GitHub Advisory Database

    Fix available

    Microsoft.NETCore.App.Runtime.linux-arm fixed in 11.0.0-rc.2

  27. Oct 13, 2026 · Catalog

    Updated

    ## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Http. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. SocketsHttpHandler can retain a header across an HTTP redirect and leak basic proxy credentials to the destination server. ## Announcement Announc

Sources

  • CVE.orgVulnerability recordCVE-2026-66822

    Insertion of sensitive information into sent data in .NET allows an unauthorized attacker to disclose information over a network.

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-66822

    30-day exploitation probability 0.7%

    first.org
  • GitHub Advisory DatabasePackage advisoryGHSA-wxxw-5cvc-53j7

    GitHub Advisory Database record mirrored by OSV.

    github.com
  • GitLab Advisory DatabasePackage advisoryCVE-2026-66822

    Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Http. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. SocketsHttpHandler can retain a Proxy-Authorization header across an HTTP redirect and leak basic proxy credentials to the destination server.

    advisories.gitlab.com
  • NCSC NetherlandsGovernment advisoryCVE-2026-66822

    Microsoft heeft kwetsbaarheden verholpen in diverse componenten van de Developer Tools, zoals .NET en Visual Studio. Een kwaadwillende kan aanvallen uitvoeren die kunnen leiden tot de categoriën schade zoals weergegeven in de onderstaande tabellen. .NET: |------------------|-----

    advisories.ncsc.nl
  • OpenSSF OSV / OSV ScannerPackage advisoryGHSA-wxxw-5cvc-53j7

    Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability

    osv.dev

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.