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CVE-2026-55009: Microsoft Exchange Server Elevation of Privilege Vulnerability

highCVSS 7.8CVE-2026-55009
Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.

CSIRTS triage

vendor: Microsoftproduct: Exchange ServerPrivilege escalation
What
Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.
Who is affected
Users of Microsoft Exchange Server.
Urgency
Remediation is urgent due to the high severity and potential for privilege escalation.
Action
Apply the latest security updates for Microsoft Exchange Server.

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Details

Source
Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity
high — CVSS 7.8
Published
2026-07-14
Exploitation
Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55009

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2026-55009coverage & exploitation statusNVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

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