# CVE-2026-54998 — Microsoft Exchange Online

> As of 2026-07-03, CVE-2026-54998 is a HIGH-severity vulnerability in Microsoft Exchange Online, CVSS v3.1 8.8, EPSS 0.6% (46.4th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-54998 as of 2026-07-03; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-07-03

## What is CVE-2026-54998?

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

The record classifies CVE-2026-54998 under weakness class [CWE-863](https://intel.threadlinqs.com/cwe/CWE-863). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 95 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 8.8 — HIGH (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **EPSS (FIRST):** 0.6% probability of exploitation in the next 30 days, higher than 46.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 6.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-02, last modified 2026-07-03

## Is CVE-2026-54998 being exploited?

It currently carries a trending score of 41 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Microsoft](https://intel.threadlinqs.com/vendors/microsoft): Exchange Online

## How to fix CVE-2026-54998

No vendor patch reference has been recorded for CVE-2026-54998 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-54998

No threat campaign in the Threadlinqs corpus currently references CVE-2026-54998, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, GitHub Security Advisories, FIRST EPSS. Last verified by Threadlinqs on 2026-07-04. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [msrc.microsoft.com — vendor advisory](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-54998)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-54998
Full detection coverage and IOCs for threats exploiting CVE-2026-54998 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp