GitHub Security Advisory: GHSA-73j8-2gch-69rq
Package: Microsoft.Bcl.Memory (NUGET)
Severity: HIGH (CVSS 7.5)
CWE: CWE-125: Out-of-bounds Read
Vulnerable versions: >= 9.0.0, <= 9.0.13
Patched in: 9.0.14

Summary: .NET Denial of Service Vulnerability

Details:
# 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

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