CVE-2026-84008: Microsoft Security Advisory CVE-2026-84008 - .NET Denial of Service Vulnerability

October 13, 2026 (updated October 19, 2026)

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Security.Cryptography.Pkcs. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

SignedCms.CheckSignature can repeatedly reparse attacker-controlled X.509 data, causing unauthenticated quadratic CPU exhaustion.

References

github.com/advisories/GHSA-846f-f764-76mx
github.com/dotnet/announcements/issues/468
github.com/dotnet/runtime/issues/135703
github.com/dotnet/runtime/security/advisories/GHSA-846f-f764-76mx
msrc.microsoft.com/update-guide/vulnerability/CVE-2026-84008
nvd.nist.gov/vuln/detail/CVE-2026-84008

Code Behaviors & Features

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