Patch tracker / KB5087423
KB5087423: Windows Server 2025 Security Update (May 2026)
KB5087423 is a Critical security update for Windows Server 2025, released 2026-05-12. It closes 66 CVEs with a maximum CVSS of 9.8. It is the largest of the 65 updates Microsoft shipped that month, by CVEs closed.
Update summary
Fixes 66 CVEs. Most severe CVSS 9.8 (Critical). EPSS exploit probability up to 2.2%. 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.
- Windows Server Update Services (WSUS) does not display error details
KB5087423 is a large rollup fixing 66 CVEs for Windows Server 2025 Server Core and Windows 11 25H2 on ARM64 and x64. The top flaw rates Critical at CVSS 9.8 with an 80 percent EPSS score, meaning exploitation is likely even though nothing here is currently in CISA KEV or tied to ransomware. Exposed systems include Server Core hosts, which are often domain controllers or infrastructure roles where a remote unauthenticated bug would be especially damaging.
Do this: Prioritize deploying KB5087423 to internet-facing and Server Core hosts first, given the CVSS 9.8 and 80 percent EPSS on the top CVE.
AI-generated from public data, 2026-07-26. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5087423
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5087423
- Released
- 2026-06-09
- Last changed
- 2026-09-26
- Changes tracked
- 4
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 KB5087423 is installed
Elevated PowerShell. No output means it is not installed.
Known issues, from Microsoft
Quoted from Microsoft's support article for KB5087423 (checked 2026-09-06). Verify against the article before acting.
Windows Server Update Services (WSUS) does not display error details
After installing KB5070893 or later updates, Windows Server Update Services (WSUS) does not display synchronization error details within its error reporting. This functionality is temporarily removed to address the Remote Code Execution Vulnerability, CVE-2025-59287 .
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 May 2026
KB5002863
9 CVEs · High · exploitedKB5002868
9 CVEs · High · exploitedKB5002870
9 CVEs · High · exploitedKB5094139
1 CVE · High · exploitedKB5094140
1 CVE · High · exploitedKB5094142
1 CVE · High · exploitedKB5094144
1 CVE · High · exploitedKB5078943
3 CVEs · CriticalThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.