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CVE-2021-34523

Exploitation: active CVSS 9.0 CRITICAL Ransomware: known use

CVSS base score: 9.0 (Critical) vendor CNA · v3.1

Score assigned by the vendor's own CVE Numbering Authority (CNA); CISA's Vulnrichment program adds a score only when the CNA omits one.

Microsoft Exchange Server Privilege Escalation Vulnerability

Vendor: Microsoft   Product: Exchange Server

Description

Microsoft Exchange Server contains an unspecified vulnerability that allows for privilege escalation.

Lifecycle Timeline

Each milestone comes from a different source, so gaps between them are gaps in what those sources publish, not evidence that nothing happened. EPSS history for this CVE holds 262 points from 2021-12-11, tracked daily from 2026-09-09; earlier points are weekly, which dates a spike to within a week. Peak probability 100.0% on 2026-08-15.

Published Applicability

CVE List v5 (CNA container) 5 affected · 0 fixed · 0 not affected

Check whether a specific version is affected →

What each source publishes about which product versions carry this vulnerability, kept as written rather than merged. Absence here means no source has published applicability data, not that nothing is affected.

Research & News Coverage

No mentions found in monitored research blogs or news feeds.

Detection & Exploitation

Scan
none published
Exploit / Pen Test
Network IDS/IPS
Host / SIEM
none published

Coverage across public collections only: Nuclei and OpenVAS NVT (scan); Snort and Suricata ET Open (network); Sigma and YARA (host/SIEM); Metasploit, Exploit-DB and public GitHub repositories (exploit). Absence here means nothing public was found, not that detection is impossible.
GitHub PoC repositories are collected automatically by PoC-in-GitHub (CC0) and are not vetted: some are fakes and some are malware. Treat them as evidence that code was published, not as code to run.
OpenVAS coverage derives from the Greenbone Community Feed, made available under the Open Database License (ODbL) v1.0; its individual Vulnerability Tests are licensed GNU GPL v2.

Microsoft Assessment

published by the affected vendor via MSRC

Microsoft Exchange Server Elevation of Privilege Vulnerability

Exploitation Less Likely
No
Yes
Important
Elevation of Privilege
Microsoft Exchange Server
2021-07-13

The vendor's own judgement about their own code, shown alongside CISA's rather than merged into it. The exploitability index is a forward-looking prediction, distinct from a CVSS severity or CISA's SSVC decision, and vendors often report observed exploitation before a CVE reaches the KEV catalog. Vendor advisory →

CISA Assessment (Vulnrichment / SSVC)

active
no
total
—
9.0 CRITICAL
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N/E:U/RL:O/RC:C
2025-02-04

KEV Catalog Status

2021-11-03
2021-11-17
Known

Listed By

SourceDateRecord
CISA KEV 2021-11-03 source record →
CISA Vulnrichment 2025-02-04 source record →

Referenced in Advisories

DateAdvisoryIssuer
2025-02-19 CISA and Partners Release Advisory on Ghost (Cring) Ransomware CISA
2025-02-19 #StopRansomware: Ghost (Cring) Ransomware CISA
2025-02-19 #StopRansomware: Ghost (Cring) Ransomware FBI
2024-07-08 People’s Republic of China (PRC) Ministry of State Security APT40 Tradecraft in Action NSA
2024-07-08 APT40 Advisory: PRC MSS Tradecraft in Action NSA

Weaponization Timeline — Offensive & Testing Tools

No exploit-tool sightings recorded for this CVE.

Evidence tiers are explained on the About page — a merged Metasploit module is far stronger evidence than a distro package mention.

External References