Patch tracker / KB5066742

KB5066742: .NET Framework 3.5 Security Update (October 2025)

KB5066742 is a Medium security update for .NET Framework 3.5, released 2025-10-14. It closes 1 CVE with a maximum CVSS of 4.8. It is the 35th largest of the 57 updates Microsoft shipped that month, by CVEs closed.

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Update summary

Medium
2025-10-14
Released
1
CVEs fixed
4.8
Max CVSS v3
Medium
Severity
Deploy this cycle
Fixes 1 CVE for .NET Framework 3.5. No confirmed in-the-wild exploitation in this set today.

Fixes 1 CVE. Most severe CVSS 4.8 (Medium). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.

Microsoft Update Catalog: download KB5066742Microsoft support article
Senserva AI Opinion for KB5066742

KB5066742 patches CVE-2025-55248 in .NET 8.0 on Linux and Mac OS and .NET 9.0 on Linux, so this is a cross-platform runtime fix rather than a Windows-only update. Severity is Medium (CVSS 4.8) with an EPSS of only 1 percent, and it is not in CISA KEV nor ransomware-linked, so this is a routine hygiene patch rather than an emergency. Exposure is limited to servers, containers, and developer machines running these specific .NET runtimes outside Windows.

Do this: Inventory your Linux and Mac OS hosts and container images for .NET 8.0 and 9.0 runtimes and apply the updated runtime during your next patch cycle.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for KB5066742

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Full tracking and change history for KB5066742

Released
2025-10-14
Last changed
2025-10-14
Changes tracked
1

Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.

Check if KB5066742 is installed

Elevated PowerShell. No output means it is not installed.

CVEs fixed by this update

Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.

CVESeverityCVSSEPSSExploited
CVE-2025-55248Medium4.8<1%No

Scope and sources

Affected products
Also released in October 2025

KB5066586

98 CVEs · Critical · exploited

KB5066780

114 CVEs · Critical · exploited

KB5066782

103 CVEs · Critical · exploited

KB5066791

98 CVEs · Critical · exploited

KB5066793

108 CVEs · Critical · exploited

KB5066835

134 CVEs · Critical · exploited

KB5070879

1 CVE · Critical · exploited

KB5070881

1 CVE · Critical · exploited

The full month, summarized: Microsoft Patch Tuesday.

Authoritative references
Official KB5066742 page (Microsoft Support)Microsoft Update CatalogMicrosoft Security Update Guide

See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
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