Patch tracker / KB5055523
KB5055523: Windows Server 2025 Security Update (April 2025)
KB5055523 is a High security update for Windows Server 2025, released 2025-04-08. It closes 82 CVEs with a maximum CVSS of 8.8. At least one of them is actively exploited (CISA KEV) and linked to ransomware, so it is urgent, and Microsoft lists 1 known issue: test it before broad deployment. The most likely of them to be attacked is CVE-2025-29824, which FIRST.org rates at 19% probability of exploitation in the next 30 days.
Our data comes from Microsoft, CISA and other public sources, and it can be wrong or out of date. If you are unsure, check the linked source before you act, and tell us when we are wrong so we can fix it.
Update summary
Fixes 82 CVEs. At least one is actively exploited (CISA KEV). Most severe CVSS 8.8 (High). EPSS exploit probability up to 19%. One is linked to ransomware. Among the top half of tracked Microsoft updates by EPSS exploit probability.
A newer security update for Windows Server 2025 (Server Core installation) has shipped since this one: KB5126646 (2026-10-13). 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.
Microsoft documents 1 known issue with this update.
- Applies to
KB5055523 is the single largest update in this entire batch of 100 at 85 CVEs, covering Windows 10 1809 and Windows Server 2019 for April 2025, with a High, CVSS 8.8 ceiling, 18 percent EPSS, a CISA KEV listing, and a confirmed ransomware linkage. A build this size touches nearly every Windows component patched that month, so compatibility testing should be thorough, but the ransomware association means testing cannot be an excuse to delay past a short window. This is the update to prioritize this month above all others in the batch.
Do this: Fast-track compatibility testing and deployment of KB5055523 given both its size and its confirmed ransomware linkage, treating it as this month's top patching priority.
AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5055523
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5055523
- Released
- 2025-04-08
- Last changed
- 2026-10-25
- Changes tracked
- 7
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.
Microsoft revised KB5055523 on 2026-09-30: CVEs fixed 85 to 82.
- 2026-08-07 CVEs fixed 85 to 82
- 2026-09-29 CVEs fixed 82 to 85
- 2026-09-30 CVEs fixed 85 to 82
Recorded by Senserva on the dates shown, from the MSRC release feed. This is what moved and when, which neither the vendor advisory nor NVD publishes.
Check if KB5055523 is installed
Elevated PowerShell. No output means it is not installed.
Known issues, from Microsoft
Quoted from Microsoft's support article for KB5055523 (checked 2026-11-04). Microsoft lists 1 known issue. Verify against the article before acting.
Citrix
Applies to
Symptom
Workaround
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 · exploitedKB5055526
77 CVEs · High · exploitedKB5055527
73 CVEs · High · exploitedKB5055528
65 CVEs · High · exploitedKB5055547
43 CVEs · High · exploitedKB5055557
55 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.