.NET Denial of Service Vulnerability

CISA KEV lists vulnerabilities known to be exploited. FIRST EPSS estimates the likelihood of exploitation in the next 30 days. An unavailable score does not mean zero risk.

Out-of-bounds read in .NET allows an unauthorized attacker to deny service over a network.

Source published

10 Mar 2026 17:05:10 UTC

Source modified

19 Jun 2026 18:17:53 UTC

Saved here

23 Oct 2026 15:48:27 UTC

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CVE Program Terms of Use

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Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · 7.5 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

Out-of-bounds read in .NET allows an unauthorized attacker to deny service over a network.

Source published

Mar 10, 2026, 5:05:10 PM (timezone not stated)

Source modified

Jun 19, 2026, 6:17:53 PM (timezone not stated)

Saved here

15 Nov 2026 08:34:22 UTC

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ENISA EUVD · source terms and attribution apply

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Source: euvd · ENISA EUVD · source terms and attribution apply. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

EUVD CVSS 3.1 · 7.5 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

Out-of-bounds read in .NET allows an unauthorized attacker to deny service over a network.

Source published

10 Mar 2026 18:18:41 UTC

Source modified

17 Jun 2026 10:25:46 UTC

Saved here

25 Oct 2026 06:17:22 UTC

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NIST NVD usage terms; underlying source attribution retained

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Source: nvd · NIST NVD usage terms; underlying source attribution retained. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS 3.1 · [email protected] · Secondary · 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.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/packages/Microsoft.NetCore.App.Runtime.win-x86) | >= 10.0.0, <= 10.0.3 | 10.0.4 ### <a name="Microsoft.Bcl.Memory 9.0.14"></a>Microsoft.Bcl.Memory 9.0.14 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.Bcl.Memory](https://www.nuget.org/packages/Microsoft.Bcl.Memory) | >= 9.0.0, <= 9.0.13 | 9.0.14 ### <a name="Microsoft.Bcl.Memory 10.0.4"></a>Microsoft.Bcl.Memory 10.0.4 Package name | Affected version | Patched version ------------ | ---------------- | ------------------------- [Microsoft.Bcl.Memory](https://www.nuget.org/packages/Microsoft.Bcl.Memory) | >= 10.0.0, <= 10.0.3 | 10.0.4 ### <a name="how-fix"></a>How to fix the issue To update the Microsoft.Bcl.Memory NuGet package, apply one of the following methods: NuGet Package Manager UI in Visual Studio: - Open the project in Visual Studio. - Right-click on the project in Solution Explorer and select "Manage NuGet Packages..." or navigate to "Project > Manage NuGet Packages". - In the NuGet Package Manager window, select the "Updates" tab. This tab lists packages with available updates from the configured package sources. - Select the package(s) to update. A specific version can be chosen from the dropdown, or the latest available version can be selected. - Click the "Update" button. Using the NuGet Package Manager Console in Visual Studio: - Open the project in Visual Studio. - Navigate to "Tools > NuGet Package Manager > Package Manager Console". - To update a specific package to its latest version, run the following Update-Package command: ``` Update-Package -Id Microsoft.Bcl.Memory ``` Using the .NET CLI (Command Line Interface): - Open a terminal or command prompt in the project's directory. - To update a specific package to its latest version, run the following command: ``` dotnet package update Microsoft.Bcl.Memory ``` Once the NuGet package reference has been updated, the application must be recompiled and redeployed. Additionally, it is recommended to update the runtime and/or SDKs, but unless the application targets .NET 9 or higher, updating the runtime and/or SDK is not a required step to patch this vulnerability. ## Other Information ### Reporting Security Issues If a potential security issue has been found in a supported version of .NET, it should be reported 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 Questions about this issue can be asked on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. Questions can be asked 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-2026-26127](https://www.cve.org/CVERecord?id=CVE-2026-26127) ### Revisions V1.0 (March 10, 2026): Advisory published.

Source published

11 Mar 2026 21:11:44 UTC

Source modified

10 Sep 2026 03:50:43 UTC

Saved here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH

### Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-73j8-2gch-69rq. This link is maintained to preserve external references. ### Original Description Out-of-bounds read in .NET allows an unauthorized attacker to deny service over a network.

Source published

10 Mar 2026 18:31:21 UTC

Source modified

10 Sep 2026 03:50:38 UTC

Saved here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

Source: osv · GitHub Advisory Database · CC-BY-4.0. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH