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

Published 2026-07-02 · last modified 2026-07-07.

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.

EPSS exploit prediction

EPSS: 0.008 (54.2th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 54.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

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.