CVE-2026-58649: .NET Information Disclosure Vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-08 · updated 2026-10-31
Weakness: CWE-346

Description

Origin validation error in .NET allows an unauthorized attacker to disclose information over a network.

Affected products

Microsoft .NET: 11.0.0-preview1, 11.0.0-preview2, 11.0.0-preview3, 11.0.0-preview4, 11.0.0-preview5, 11.0.0-preview6 (+1)
Microsoft .Net Sdk: from 8.0.100 before 8.0.130; from 8.0.200 before 8.0.424; from 9.0.100 before 9.0.120; from 9.0.200 before 9.0.317; from 10.0.100 before 10.0.111; from 10.0.200 before 10.0.400 — fixed in 8.0.130, 8.0.424, 9.0.120, 9.0.317, 10.0.111, 10.0.400
Microsoft Visual Studio 2022 version 17.14: from 17.14.0 before 17.14.40 — fixed in 17.14.40
Microsoft Visual Studio 2026 version 18.9: from 18.9.0 before 18.9.3 — fixed in 18.9.3
Microsoft .NET 10.0 runtime: from 10.0.0 before 10.0.111, 10.0.400 — fixed in 10.0.111, 10.0.400
Microsoft .NET 11.0 runtime: from 11.0.0 before 11.0 RC1 — fixed in 11.0 RC1
Microsoft .NET 8.0 runtime: from 8.0.0 before 8.0.130, 8.0.424 — fixed in 8.0.130, 8.0.424
Microsoft .NET 9.0 runtime: from 9.0.0 before 9.0.120, 9.0.317 — fixed in 9.0.120, 9.0.317
Microsoft Visual Studio 2022 version 17.14: from 17.14.0 before 17.14.40 — fixed in 17.14.40
Microsoft Visual Studio 2026 version 18.9: from 18.9.0 before 18.9.3 — fixed in 18.9.3

How to fix

Upgrade to a fixed version: Microsoft .Net Sdk 8.0.130, 8.0.424, 9.0.120, 9.0.317; Microsoft Visual Studio 2022 version 17.14 17.14.40; Microsoft Visual Studio 2026 version 18.9 18.9.3; Microsoft .NET 10.0 runtime 10.0.111, 10.0.400; Microsoft .NET 11.0 runtime 11.0 RC1; Microsoft .NET 8.0 runtime 8.0.130, 8.0.424; Microsoft .NET 9.0 runtime 9.0.120, 9.0.317; Microsoft Visual Studio 2022 version 17.14 17.14.40; Microsoft Visual Studio 2026 version 18.9 18.9.3. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-58649

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