Threat Intelligence / CVE / CVE-2023-21529

CVE-2023-21529 — Microsoft Exchange Server

CVSS v3.1 8.8 (HIGH) · EPSS 36.6% (higher than 97.1% of all scored CVEs) · Priority 8.3/10 · Published 2023-02-14

As of 2024-11-21, CVE-2023-21529 is a HIGH-severity vulnerability in Microsoft Exchange Server, CVSS v3.1 8.8, EPSS 36.6% (97.1th percentile). Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2023-21529, most recently “CISA KEV Catalog Update: Seven Actively Exploited Vulnerabilities Added 2026-04-13 (Microsoft, Adobe, Fortinet)”.

Last updated: 2024-11-21

What is CVE-2023-21529?

Microsoft Exchange Server Remote Code Execution Vulnerability

The record classifies CVE-2023-21529 under weakness classes CWE-502, NVD-CWE-noinfo. 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. 4 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 1307 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
EPSS (FIRST): 36.6% probability of exploitation in the next 30 days, higher than 97.1% of all scored CVEs
CISA KEV: Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority: 8.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published: 2023-02-14, last modified 2024-11-21

Is CVE-2023-21529 being exploited?

It currently carries a trending score of 29 in the Threadlinqs vulnerability feed.

Affected products and versions

Microsoft: Exchange Server 2013, Exchange Server 2016, Exchange Server 2019

Showing 3 of 4 recorded product entries.

How to fix CVE-2023-21529

Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-21529. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2023-21529

2 tracked threats in the Threadlinqs corpus reference CVE-2023-21529, either in the campaign’s CVE list or as an indicator on the campaign record.

CISA KEV Catalog Update: Seven Actively Exploited Vulnerabilities Added 2026-04-13 (Microsoft, Adobe, Fortinet) — CRITICAL · 2026-04-13
Storm-1175 Medusa Ransomware Zero-Day Exploitation Campaign (CVE-2026-23760, CVE-2025-10035) — CRITICAL · 2026-04-06

Sources

Seeded from nvd and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

msrc.microsoft.com

Full detection coverage & IOCs for threats exploiting CVE-2023-21529 are available via the Threadlinqs MCP server (Purple tier). View plans →

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