Schedule normally
No exploitation observed as of 2026-09-29: not in the CISA KEV catalog, EPSS 3%.
Fixed by KB5103212 and 3 more (by build, listed below). Download from the Microsoft Update Catalog, or deploy via Windows Update, Intune, or WSUS.
Do this now: Deploy with your normal update cycle. This page refreshes daily; the verdict changes the day the data does.

Patch tracker / CVE reference / CVE-2026-45501

CVE-2026-45501

CVE-2026-45501 is a Microsoft vulnerability that Microsoft rates Important, with a CVSS score of 6.5 (Medium). Microsoft has shipped the fix: deploy one of the 4 updates below from the Microsoft Update Catalog, and see where this CVE sits against the rest on the patch tracker.

Risk summary

Medium
6.5
CVSS v3
2.5%
EPSS, 30 days
Medium
Severity

Not in the CISA KEV catalog. EPSS exploit probability 2.5%. CVSS 6.5 (Medium).

This CVE is among the lower half of tracked Microsoft CVEs by EPSS exploit probability.

Senserva AI Opinion for CVE-2026-45501

CVE-2026-45501 is a spoofing flaw in on-premises Microsoft Exchange Server, hitting Subscription Edition RTM plus the current cumulative updates for the 2016 and 2019 lines (CU23 and CU15). Spoofing on Exchange typically means an attacker can forge identity or content in a way that supports phishing or authentication trickery against your mail environment. Severity is rated High with a CVSS of 8.8, though EPSS puts exploit probability at only 6 percent, and it is not in CISA KEV or tied to ransomware.

Do this: Inventory your on-prem Exchange servers and apply Microsoft's security update for the Subscription Edition, 2016 CU23, and 2019 CU15 builds you are running.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2026-45501

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

Official patch(es) for CVE-2026-45501

Lower priority: patch in your normal cycle. In Intune or Defender, confirm whether the fixing updates KB5103212, KB5103213, KB5103214, KB5103215 are installed across the affected products. Senserva does this automatically across your tenant and flags every missing patch.

Apply the Microsoft security updates below to fix CVE-2026-45501. Each KB page carries the Microsoft Update Catalog download, Microsoft's known issues for the update, a copy-paste PowerShell check for whether it is installed, and the Senserva AI read.

KB5103212KB5103213KB5103214KB5103215

Scope and sources

Affected products
Fixed by the same updates
CVE-2026-45500CVE-2026-45502CVE-2026-55008CVE-2026-45504CVE-2026-55005CVE-2026-45503CVE-2026-47631CVE-2026-55006
Authoritative references
Official CVE record (cve.org)NVD detailMicrosoft MSRCFIRST.org EPSS

Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.

New to a term on this page? CVE, KB, KEV, CVSS, and EPSS are each explained once, on the Senserva security lexicon. Reference: Microsoft CVE and vulnerability management and the Microsoft patching guide.
All information provided as is, without warranty; verify against the vendor advisory before acting. All information and usage is subject to the Senserva EULA. Data notice and terms.