CVE-2026-25667

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 3.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-19 · updated 2026-06-17
Weakness: CWE-400

Description

ASP.NET Core Kestrel in Microsoft .NET 8.0 before 8.0.22 and .NET 9.0 before 9.0.11 allows a remote attacker to cause excessive CPU consumption by sending a crafted QUIC packet, because of an incorrect exit condition for HTTP/3 Encoder/Decoder stream processing.

Affected products

Microsoft .NET: from 8.0.0 before 8.0.22; from 9.0.0 before 9.0.11 — fixed in 8.0.22, 9.0.11

How to fix

Upgrade to a fixed version: Microsoft .NET 8.0.22, 9.0.11. Check the vendor advisory for mitigations.

References

https://github.com/IsaJafarov/Kestrel-DoS
https://github.com/IsaJafarov/Q3Fuzz
https://github.com/dotnet/aspnetcore/commit/96ccc40a0e095424b19506e8268b9b1a3e23d6a7#diff-667d5b3693f93a0f706ab211428998b210862f9b885d917104d2013118312626

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