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A GitHub-reviewed security advisory, not necessarily under active exploitation the way our CISA KEV advisories are, but a real, disclosed vulnerability in an open-source dependency.
Affected packages
Vulnerable: >= 8.0.0-0, < 8.0.2
Patched in 8.0.2
Vulnerable: >= 9.0.0-0, < 9.0.24
Patched in 9.0.24
Vulnerable: >= 10.0.0-0, < 10.0.15
Patched in 10.0.15
Vulnerable: >= 11.0.0-0, < 11.0.0
Patched in 11.0.0
Details
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 for this issue can be found at https://github.com/dotnet/announcements/issues/501
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:CThe tables list affected package versions and fixed versions. These are independently versioned NuGet packages, not runtime patch versions.
| Package | Affected version | Patched version |
|---|---|---|
| System.Formats.Cbor | >= 8.0.0-0, < 8.0.2 | 8.0.2 |
| Package | Affected version | Patched version |
|---|---|---|
| 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.
| Package | Affected version | Patched version |
|---|---|---|
| System.Formats.Cbor | >= 10.0.0-0, < 10.0.15 | 10.0.15 |
| Package | Affected version | Patched version |
|---|---|---|
| System.Formats.Cbor | >= 11.0.0-0, < 11.0.0 | 11.0.0 |
Check the application's System.Formats.Cbor package reference against the affected ranges above. Updating only the installed runtime does not update this independently referenced package.
Update each applicable package reference to its patched version listed above, then rebuild and redeploy the application. Updating only the installed runtime does not update an application's standalone package references.
If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.
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.
You can ask questions about this issue 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. You can ask questions in the linked discussion issue.
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.
V1.0 (November 10, 2026): Advisory published.
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