GHSA-qvhc-9v3j-5rfw — System.Security.Cryptogra…
GHSA-qvhc-9v3j-5rfw is a security vulnerability in System.Security.Cryptography.Cose. A fix is available for System.Security.Cryptography.Cose — see the affected versions and patch details below.
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-qvhc-9v3j-5rfw.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
System.Security.Cryptography.Cose.NETSystem.Security.Cryptography.Cose.NETSystem.Security.Cryptography.CoseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Microsoft Security Advisory CVE-2026-21218 | .NET Security Feature Bypass Vulnerability
<a name="executive-summary"></a>Executive summary
Microsoft is releasing this security advisory to provide information about a vulnerability in .NET 8.0, .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.
An attacker could exploit this vulnerability by crafting a malicious payload that bypasses the security checks in the affected System.Security.Cryptography.Cose versions, potentially leading to unauthorized access or data manipulation.
Announcement
Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/380
<a name="mitigation-factors"></a>Mitigation factors
If your application does not use System.Security.Cryptography.Cose it is not affected. By default, no .NET applications reference this component.
<a name="affected-packages"></a>Affected Packages
The vulnerability affects any Microsoft .NET project if it uses any of affected packages versions listed below
<a name=".NET 10"></a>.NET 10
| Package name | Affected version | Patched version |
|---|---|---|
| System.Security.Cryptography.Cose | >= 10.0.0, <= 10.0.2 | 10.0.3 |
<a name=".NET 9"></a>.NET 9
| Package name | Affected version | Patched version |
|---|---|---|
| System.Security.Cryptography.Cose | >= 9.0.0, <= 9.0.12 | 9.0.13 |
<a name=".NET 8"></a>.NET 8
| Package name | Affected version | Patched version |
|---|---|---|
| System.Security.Cryptography.Cose | >= 8.0.0, <= 8.0.1 | 8.0.2 |
Advisory FAQ
<a name="how-affected"></a>How do I know if I am affected?
If an affected package listed in affected software or affected packages, you're exposed to the vulnerability.
<a name="how-fix"></a>How do I fix the issue?
To update the Using the System.Security.Cryptography.Cose NuGet package, use one of the following methods:
NuGet Package Manager UI in Visual Studio:
- Open your project in Visual Studio.
- Right-click on your 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 your configured package sources.
- Select the package(s) you wish to update. You can choose a specific version from the dropdown or update to the latest available version.
- Click the "Update" button.
Using the NuGet Package Manager Console in Visual Studio:
- Open your project in Visual Studio.
- Navigate to "Tools > NuGet Package Manager > Package Manager Console".
- To update a specific package to its latest version, use the following Update-Package command:
Update-Package -Id System.Security.Cryptography.Cose
Using the .NET CLI (Command Line Interface):
- Open a terminal or command prompt in your project's directory.
- To update a specific package to its latest version, use the following add package command:
dotnet add package System.Security.Cryptography.Cose
Once you have updated the nuget package reference you must recompile and deploy your application. Additionally we recommend you update your runtime and/or SDKs, but it is not necessary to patch the vulnerability.
Other Information
Reporting Security Issues
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.
Support
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.
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
Acknowledgements
vcsjones with GitHub
Revisions
V1.0 (February 10, 2026): Advisory published.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | System.Security.Cryptography.Cose | ≥ 8.0.0&&< 8.0.2 | 8.0.2dotnet add package System.Security.Cryptography.Cose --version 8.0.2 |
| .NETNuGet | System.Security.Cryptography.Cose | ≥ 9.0.0&&< 9.0.13 | 9.0.13dotnet add package System.Security.Cryptography.Cose --version 9.0.13 |
| .NETNuGet | System.Security.Cryptography.Cose | ≥ 10.0.0&&< 10.0.3 | 10.0.3dotnet add package System.Security.Cryptography.Cose --version 10.0.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for System.Security.Cryptography.Cose, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update System.Security.Cryptography.Cose to 8.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-qvhc-9v3j-5rfw is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-qvhc-9v3j-5rfw can be triaged on real exposure rather than presence alone.
Tailored to GHSA-qvhc-9v3j-5rfw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is GHSA-qvhc-9v3j-5rfw in your dependencies?
O3 Security finds GHSA-qvhc-9v3j-5rfw across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.