🛡️ CVE-2026-26127 — .net

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-125 NVD
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

.NET Denial of Service Vulnerability

# 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

------------ | ---------------- | -------------------------

[Microsoft.NetCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-x64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-x64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-arm64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-x64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x64) | >= 9.0.0, <= 9.0.13 | 9.0.14

[Microsoft.NetCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x86) | >= 9.0.0, <= 9.0.13 | 9.0.14

<a name=".NET 10"></a>.NET 10

Package name | Affected version | Patched version

------------ | ---------------- | -------------------------

[Microsoft.NetCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-arm64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-arm64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-musl-x64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.linux-x64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-arm64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.osx-x64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-arm64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NetCore.App.Runtime.win-x64) | >= 10.0.0, <= 10.0.3 | 10.0.4

[Microsoft.NetCore.App.Runtime.win-x86](https://www.nuget.org/packag

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Weakness class

CVE-2026-26127 is classified as CWE-125: Out-of-bounds Read. The code reads past the limits of a buffer, exposing adjacent memory contents or crashing the process.

Affected software

CVE-2026-26127 is recorded against 17 packages.

  • .net (from 9.0.0 up to 9.0.14)
  • bcl.memory (from 10.0.0 up to 10.0.4)
  • dotnet
  • dotnet-sdk
  • microsoft.bcl.memory (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-arm (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-arm64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-musl-arm (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-musl-arm64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-musl-x64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.linux-x64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.osx-arm64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.osx-x64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.win-arm (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.win-arm64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.win-x64 (from 10.0.0 up to 10.0.4)
  • microsoft.netcore.app.runtime.win-x86 (from 10.0.0 up to 10.0.4)

Timeline and source

Published on 10 March 2026 and last revised on 17 June 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

msrc.microsoft.com

CVE-2026-26127 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-125
Public Exploit ✅ No
Source NVD
Published 2026-03-10
Updated 2026-08-12
Modified 2026-06-17
Fix URL N/A

Affected Packages

Software From version Fixed in
.net 9.0.0 9.0.14
bcl.memory 10.0.0 10.0.4
dotnet — —
dotnet-sdk — —
microsoft.bcl.memory 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-arm 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-arm64 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-musl-arm 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-musl-arm64 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-musl-x64 10.0.0 10.0.4
microsoft.netcore.app.runtime.linux-x64 10.0.0 10.0.4
microsoft.netcore.app.runtime.osx-arm64 10.0.0 10.0.4
microsoft.netcore.app.runtime.osx-x64 10.0.0 10.0.4
microsoft.netcore.app.runtime.win-arm 10.0.0 10.0.4
microsoft.netcore.app.runtime.win-arm64 10.0.0 10.0.4
microsoft.netcore.app.runtime.win-x64 10.0.0 10.0.4
microsoft.netcore.app.runtime.win-x86 10.0.0 10.0.4

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