Patch tracker / KB5103213
KB5103213: Microsoft Exchange Server Subscription Security Update (July 2026)
KB5103213 is a Critical security update for Microsoft Exchange Server Subscription, released 2026-07-14. It closes 11 CVEs with a maximum CVSS of 9.6. The most likely of them to be attacked is CVE-2026-55005, which FIRST.org rates at 20% probability of exploitation in the next 30 days.
Update summary
Fixes 11 CVEs. Most severe CVSS 9.6 (Critical). EPSS exploit probability up to 20%. Among the top half of tracked Microsoft updates by EPSS exploit probability.
A newer security update for Microsoft Exchange Server 2016 Cumulative Update 23 has shipped since this one: KB5121573 (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 KB5103213 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.
KB5103213 is a Security Update for Exchange Server 2019 Cumulative Update 15, shipped in the July 2026 Patch Tuesday cycle. The per-update CVE breakdown is still provisional because Microsoft has not published the detail for this cycle, and the release document maps no named zero-days here. Exchange remains a high-value target regardless of headline severity, so any on-premises mailbox server running CU15 is in scope even without a confirmed critical flaw yet.
Do this: Stage KB5103213 on a non-production Exchange 2019 CU15 server now and confirm the CVE detail once Microsoft publishes it before scheduling the production rollout.
AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for KB5103213
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5103213
- Released
- 2026-07-14
- Last changed
- 2026-07-29
- Changes tracked
- 2
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 KB5103213 on 2026-07-29: CVEs fixed 4 to 11.
- 2026-07-29 CVEs fixed 4 to 11
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 KB5103213 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.
| CVE | Severity | CVSS | EPSS | Exploited |
|---|---|---|---|---|
| CVE-2026-55008 | Critical | 9.6 | 20% | No |
| CVE-2026-45504 | High | 8.8 | 20% | No |
| CVE-2026-55005 | High | 8.8 | 20% | No |
| CVE-2026-45503 | High | 8.1 | 20% | No |
| CVE-2026-47631 | High | 8.1 | 20% | No |
| CVE-2026-55006 | High | 7.8 | 20% | No |
| CVE-2026-55009 | High | 7.8 | 20% | No |
| CVE-2026-45583 | High | 7.5 | 20% | No |
| CVE-2026-45501 | Medium | 6.5 | 20% | No |
| CVE-2026-45500 | Medium | 6.1 | 20% | No |
| CVE-2026-45502 | Medium | 5.0 | 20% | No |
Scope and sources
- Affected products
- Also released in July 2026
KB5099444
185 CVEs · Critical · exploitedKB5099445
174 CVEs · Critical · exploitedKB5099535
261 CVEs · Critical · exploitedKB5099536
389 CVEs · Critical · exploitedKB5099538
312 CVEs · Critical · exploitedKB5099539
314 CVEs · Critical · exploitedKB5099540
326 CVEs · Critical · exploitedKB5101649
383 CVEs · Critical · 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.