Patch tracker / CVE reference / CVE-2026-45503
CVE-2026-45503
CVE-2026-45503 is a Microsoft vulnerability that Microsoft rates Important, with a CVSS score of 8.1 (High). 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
Not in the CISA KEV catalog. EPSS exploit probability 2.5%. CVSS 8.1 (High).
This CVE is among the lower half of tracked Microsoft CVEs by EPSS exploit probability.
The exploit probability of CVE-2026-45503 is RISING: EPSS 20% to 70% on 2026-08-03.
Drawn by Senserva Vivid from the Senserva change record. Hover any point for its date and value.
- 2026-07-17 CVSS 8.1 to 8.8; EPSS first scored at 5.6%
- 2026-07-24 CVSS 8.8 to 6.5; CVSS 6.5 to 8.8; EPSS 5.6% to 20.3%
- 2026-07-29 CVSS 8.8 to 9.6
- 2026-08-03 EPSS 20.3% to 70.3%
Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.
This is an information disclosure flaw in on-premises Exchange Server carrying a High severity rating with a CVSS score of 8.8, which is unusually elevated for a disclosure-only issue and suggests it can expose sensitive mailbox or configuration data. Exposed systems include Exchange 2016 CU23, Exchange 2019 CU15, and the Subscription Edition RTM, so most organizations still running Exchange on-premises are in scope. It is not in CISA KEV and has no confirmed ransomware use, but the 20 percent EPSS score is meaningfully above baseline for an internet-facing mail platform.
Do this: Apply the Microsoft security update to your Exchange 2016 CU23, 2019 CU15, and Subscription Edition RTM servers, prioritizing any instances with externally reachable OWA or ECP.
AI-generated from public data, 2026-07-25. Verify against the vendor advisory before acting.
Senserva AI Opinion and rich prompt for CVE-2026-45503
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Official patch(es) for CVE-2026-45503
Moderate priority: schedule it in your normal patch 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-2026-45503. 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.
Scope and sources
- Affected products
- Fixed by the same updates
- Authoritative references
Want every Microsoft CVE and the patches that fix it, ranked by real-world risk? See the Microsoft Patch Tracker.