.NET Denial of Service Vulnerability
Date: 2026-03
Affected: nuget/Microsoft.NetCore.App.Runtime.win-arm64, nuget/Microsoft.NetCore.App.Runtime.win-x86, nuget/Microsoft.NetCore.App.Runtime.win-x64
Attack vector: dos
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-26127
CWE: CWE-125
CVSS: 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

# 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.R


Mitigations:

Architectural layers (MAESTRO):