Patch tracker / KB5055609
KB5055609: Windows Server 2019 Security Update (April 2025)
KB5055609 is a High security update for Windows Server 2019, released 2025-04-08. It closes 39 CVEs with a maximum CVSS of 8.8. At least one of them is actively exploited (CISA KEV) and linked to ransomware, so this is a deploy-first update. The most likely of them to be attacked is CVE-2025-26663, which FIRST.org rates at 14% probability of exploitation in the next 30 days.
Update summary
Fixes 39 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 8.8 (High). EPSS exploit probability up to 14%. One is linked to ransomware. Among the top half of tracked Microsoft updates by EPSS exploit probability.
A newer security update for Windows 10 Version 1809 for 32-bit Systems has shipped since this one: KB5094041 (2026-08-11). For cumulative update families the newer package includes these fixes, so installing that one is usually the shorter path. Verify against your own update rings before you skip this package.
We checked Microsoft's support article for KB5055609 on 2026-08-11 and it lists no known issues. Read the article before broad deployment; Microsoft adds issues as reports come in, and we re-check on every refresh.
KB5055609 is a narrower April 2025 update at 39 CVEs for Windows 10 1809 and Windows Server 2019, again High severity at CVSS 8.8 with 18 percent EPSS, sharing the CISA KEV listing and ransomware linkage that define this month's whole update family. It is one of the smaller builds in this batch, so double-check it covers the specific ransomware-linked CVEs relevant to your environment. A smaller CVE list is not a reason to treat this as optional.
Do this: Verify KB5055609 covers the ransomware-linked CVEs relevant to your fleet, escalating to a broader April 2025 build if it does not.
AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5055609
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5055609
- Released
- 2025-04-08
- Last changed
- 2026-08-12
- Changes tracked
- 3
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 KB5055609 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.
Scope and sources
- Affected products
- Also released in April 2025
KB5055518
59 CVEs · High · exploitedKB5055519
73 CVEs · High · exploitedKB5055521
60 CVEs · High · exploitedKB5055523
82 CVEs · High · exploitedKB5055526
77 CVEs · High · exploitedKB5055527
73 CVEs · High · exploitedKB5055528
65 CVEs · High · exploitedKB5055547
43 CVEs · High · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.