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 1355 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)
- 59.2% probability of exploitation in the next 30 days, higher than 99.1% of all scored CVEs
- CISA KEV
- Listed since 2026-04-13, federal remediation deadline 2026-04-27 — used in known ransomware campaigns
- Threadlinqs priority
- 10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
- Published
- 2023-02-14, last modified 2026-08-19
Is CVE-2023-21529 being exploited?
CISA added CVE-2023-21529 to the Known Exploited Vulnerabilities catalog on 2026-04-13, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-04-27 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. Weaponised exploit code for CVE-2023-21529 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 53 in the Threadlinqs vulnerability feed.
- trickest/cve (trickest)
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. Because CVE-2023-21529 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-04-27. 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
3 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.
- Emperador Ransomware Group Claims 3.9GB Data Theft from AB InBev (Budweiser, Corona Maker) - Unverified $1M Bitcoin Extortion — MEDIUM · 2026-10-26
- 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
Enriched from CVE.org, FIRST EPSS, CISA KEV, public proof-of-concept repositories. Last verified by Threadlinqs on .