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CVE-2026-54998: Microsoft Exchange Online Elevation of Privilege Vulnerability

highpublic exploitCVSS 8.8CVE-2026-54998
Incorrect authorization in Microsoft Exchange Online allows an authorized attacker to elevate privileges over a network.

CSIRTS triage

vendor: Microsoftproduct: Exchange OnlinePrivilege escalation
What
Incorrect authorization allows an authorized attacker to elevate privileges.
Who is affected
Users of Microsoft Exchange Online.
Urgency
High urgency for remediation due to high severity and potential for privilege escalation.
Action
Implement the recommended security measures for CVE-2026-54998.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source
Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity
high — CVSS 8.8
Published
2026-07-02
Exploitation
Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-54998

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-2026-54998coverage & exploitation statusNVD · CVE.org

Same CVEs, other sources

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

Recent advisories for Microsoft Exchange Online

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

More from Microsoft Security Response Center