What is CVE-2026-54998?

CVE-2026-54998 is a high-severity vulnerability in Microsoft Exchange Online, classified under Incorrect Authorization. CVSS score: 8.8/10. Published 2026-07-02.

How severe is CVE-2026-54998?

High severity. CVSS v3 base score is 8.8 out of 10.

Is CVE-2026-54998 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Auth bypass in Microsoft Exchange Online

CVE-2026-54998

Incorrect authorization in Microsoft Exchange Online allows an authorized attacker to elevate privileges over a network.

Vulnerability class: Broken Access Control

EPSS: 0.006 (47.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Affected products

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

Public proof-of-concept exploits

sentinel-aidefense/CVE-2026-54998-exp

References

Microsoft Exchange Online Elevation of Privilege Vulnerability (vendor-advisory, patch, Vendor Advisory)

Frequently asked questions

What is CVE-2026-54998?: CVE-2026-54998 is a high-severity vulnerability in Microsoft Exchange Online, classified under Incorrect Authorization. CVSS score: 8.8/10. Published 2026-07-02.
How severe is CVE-2026-54998?: High severity. CVSS v3 base score is 8.8 out of 10.
Is CVE-2026-54998 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.