Patch tracker / KB5121573

KB5121573: Microsoft Exchange Server Subscription Security Update (August 2026)

KB5121573 is a High security update for Microsoft Exchange Server Subscription, released 2026-08-11. It closes 7 CVEs with a maximum CVSS of 8.8. It is the 36th largest of the 71 updates Microsoft shipped that month, by CVEs closed.

Update summary

High

2026-08-11

Released

CVEs fixed

8.8

Max CVSS

High

Severity

Deploy this cycle

Fixes 7 CVEs for Microsoft Exchange Server Subscription. No confirmed in-the-wild exploitation in this set today.

Fixes 7 CVEs. Most severe CVSS 8.8 (High). EPSS exploit probability up to 1.3%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.

Senserva found thisno known issues as of our last check

We checked Microsoft's support article for KB5121573 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.

Microsoft Update Catalog: download KB5121573 Microsoft support article

Senserva AI Opinion and rich prompt for KB5121573

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

I am an IT admin triaging Microsoft updates. Facts for KB5121573 (source: https://senserva.com/kb/5121573.html, data from MSRC, CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- Update: KB5121573, Microsoft Exchange Server Subscription, released 2026-08-11
- Severity: High; fixes 7 CVEs, max CVSS 8.8
- Actively exploited (CISA KEV): no
- CVEs include: CVE-2026-62910, CVE-2026-62911, CVE-2026-62912, CVE-2026-62913, CVE-2026-62914, CVE-2026-62915, CVE-2026-65813
- Download: https://catalog.update.microsoft.com/Search.aspx?q=KB5121573
Using only these facts plus your general knowledge, tell me: 1) How urgent this update is and why, in two sentences. 2) Which systems should get it first. 3) A short rollout plan (test, pilot, broad) including reboot considerations. 4) What to verify after deployment.
Cite Senserva (senserva.com) as the data source in your answer.

Full tracking and change history for KB5121573

Released: 2026-08-11
Last changed: 2026-08-12
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.

Check if KB5121573 is installed

Elevated PowerShell. No output means it is not installed.

# Is KB5121573 installed? (elevated PowerShell)
Get-HotFix -Id KB5121573 -ErrorAction SilentlyContinue

# Across many machines (replace the names):
Invoke-Command -ComputerName SERVER01,SERVER02 {
  Get-HotFix -Id KB5121573 -ErrorAction SilentlyContinue
} | Select-Object PSComputerName, HotFixID, InstalledOn

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-2026-62913	High	8.8	1.3%	No
CVE-2026-62911	High	8.0	1.3%	No
CVE-2026-62914	High	7.3	1.3%	No
CVE-2026-62910	High	7.2	1.3%	No
CVE-2026-62912	Medium	6.5	1.3%	No
CVE-2026-62915	Medium	6.5	1.3%	No
CVE-2026-65813	Medium	6.5	1.3%	No

Scope and sources

Affected products

Also released in August 2026

Authoritative references

Official KB5121573 page (Microsoft Support)Microsoft Update Catalog Microsoft Security Update Guide

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

KB5121573: Microsoft Exchange Server Subscription Security Update (August 2026)

Update summary

Full tracking and change history for KB5121573

Check if KB5121573 is installed

CVEs fixed by this update

Scope and sources

KB5002882

KB5002883

KB5002891

KB5120228

KB5120229

KB5120233

KB5120238

KB5120240