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Microsoft Security Response CenterCVE-2026-55009

Microsoft Exchange Server Elevation of Privilege Vulnerability

Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.

Read the vendor bulletin Get alerts for Microsoft Exchange Server 2016 Cumulative Update
7.8CVSS out of 10High severity
Scope

What the vendor says is affected

  • Microsoft Exchange Server 2016 Cumulative Update 23
  • Microsoft Exchange Server 2019 Cumulative Update 14
  • Microsoft Exchange Server Subscription Edition RTM
  • Microsoft Exchange Server 2019 Cumulative Update 15

Versions the vendor lists as fixed

  • 15.01.2507.071
  • 15.02.1544.043
  • 15.02.2562.045
  • 15.02.1748.048
Next step

What the vendor recommends

Install KB5103215. Install KB5103214. Install KB5103212. Install KB5103213.

Review the complete instructions on the vendor's site
Timeline

When this advisory changed

  1. Published by Microsoft Security Response Center

    The publication date reported by the vendor.

  2. Added to SecurityAlert

    We collected the advisory from the official source.

Vulnerabilities

CVEs named in this advisory

CVE-2026-55009View CVSS, KEV, EPSS, and threat context
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