CVE-2026-70186: Microsoft.AspNetCore.App.Runtime Denial of Service Vulnerability
Summary
CVE-2026-70186: Microsoft Security Advisory CVE-2026-70186 - ASP.NET Core Denial of Service Vulnerability. Affects Microsoft.AspNetCore.App.Runtime.linux-arm across 3 version ranges.
>= 8.0.0, < 8.0.32
>= 9.0.0, < 9.0.21
>= 10.0.0, < 10.0.13
Fixed in 8.0.32, 9.0.21 or 10.0.13, depending on the release line you run. How to fix ↓
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Background
Microsoft.AspNetCore.App.Runtime is a collection of libraries and tools designed for building web applications and services using the ASP.NET Core framework. It provides essential functionalities such as routing, middleware, and server capabilities, enabling developers to create robust and scalable applications. However, certain versions of this package are vulnerable to a denial of service (DoS) attack, which can severely impact application availability and performance.
Vulnerability Detail
The vulnerability identified as CVE-2026-70186 allows unauthenticated remote attackers to exploit the Kestrel connection handling in ASP.NET Core by sending crafted HTTP/3 reset or abort sequences. This can lead to a deadlock situation, causing excessive blocked-thread creation and exhausting server resources. As a result, legitimate users may experience service outages, leading to a denial of service. The vulnerability is classified under CWE-833, which pertains to deadlock issues.
How To Fix
Latest published version: 10.0.13 as of 23 Oct 2026
The newest release already contains this fix.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
>= 8.0.0, < 8.0.328.0.32 -
>= 9.0.0, < 9.0.219.0.21
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
As a temporary workaround, you can limit the number of concurrent connections or implement rate limiting on your server to mitigate the impact of potential attacks until the package is updated.
Conclusion
CVE-2026-70186 is a significant denial of service vulnerability affecting multiple versions of the Microsoft.AspNetCore.App.Runtime package. It is crucial for developers to update to the patched versions to ensure their applications remain secure and available. Implementing workarounds can provide temporary relief until the updates are applied.
See every vulnerability recorded for Microsoft.AspNetCore.App.Runtime.linux-arm →
FAQ
If you are using any version of the Microsoft.AspNetCore.App.Runtime package listed in the affected packages section, your application is vulnerable.
Consider implementing rate limiting or connection throttling to reduce the risk of exploitation until you can apply the patch.
Yes, you can use Vulert, which monitors and alerts in real-time for open-source vulnerabilities in your software. You can check your application against known vulnerabilities using the Vulert playground without requiring any signup.
The CVSS score for this vulnerability is 7.5, indicating a high severity level.
You can find detailed information in the Microsoft Security Advisory and on the CVE website for CVE-2026-70186.
References
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