CVE-2026-118747

## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in .NET. This advisory provides guidance on updating affected applications and components. Colliding CBOR map keys can hash-flood uniqueness checks; the fix uses seeded Marvin hashing. ## Announcement Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/501 ## CVSS Details - **Version:** 3.1 - **Severity:** High - **Score:** 7.5 (base score) - **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` - **Weakness:** CWE-407 ## Affected Platforms - **Platforms:** Any supported OS - **Architectures:** All ## <a name="affected-packages"></a>Affected Packages The tables list affected package versions and fixed versions. These are independently versioned NuGet packages, not runtime patch versions. ### 8.0 - standalone packages Package | Affected version | Patched version --- | --- | --- [System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 8.0.0-0, < 8.0.2 | 8.0.2 ### 9.0 - standalone packages Package | Affected version | Patched version --- | --- | --- [System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 9.0.0-0, < 9.0.24 | 9.0.24 Update 9.0 applications to System.Formats.Cbor 9.0.24; 9.0.23 is not a fix. The fixed 10.0.15 package, which includes a net9.0 target, remains an alternative. ### 10.0 - standalone packages Package | Affected version | Patched version --- | --- | --- [System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 10.0.0-0, < 10.0.15 | 10.0.15 ### 11.0 - standalone packages Package | Affected version | Patched version --- | --- | --- [System.Formats.Cbor](https://www.nuget.org/packages/System.Formats.Cbor) | >= 11.0.0-0, < 11.0.0 | 11.0.0 ## Advisory FAQ ### <a name="how-affected"></a>How do I know if I am affected? Check the application's System.Formats.Cbor package reference against the affecte