OnlyPatch
Microsoft Exchange Server

CVE-2021-28481 — Microsoft Exchange Server Remote Code Execution Vulnerability

Critical CVSS 9.8 EPSS 0.36486 2021-04 archive

Executive Summary

None

Overview

9.8
CVSS CRITICAL
Critical
MS Severity
Not Exploited
MS Exploit Status
More Likely
MS Exploit Likelihood
Category Remote Code Execution
Released Apr 13 2021
Last Updated Apr 13 2021
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.36486 — 0.98353 percentile
NVD CVSS 9.8 CRITICAL — matches MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
ATTACK VECTOR
Network
ATTACK COMPLEXITY
Low
PRIVILEGES REQUIRED
None
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
High
INTEGRITY
High
AVAILABILITY
High
EXPLOIT CODE MATURITY
Unproven
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 8.5

EPSS Score

0.36486
probability of exploitation in the next 30 days
0.98353 percentile - updated 2026-08-14
View on FIRST.org

Affected Products

5 affected products
Product KB Article Severity Impact Restart Required
Microsoft Exchange Server 2013 Cumulative Update 23 5001779 (Security Update) Critical Remote Code Execution Yes
Microsoft Exchange Server 2016 Cumulative Update 19 5001779 (Security Update) Critical Remote Code Execution Yes
Microsoft Exchange Server 2016 Cumulative Update 20 5001779 (Security Update) Critical Remote Code Execution Yes
Microsoft Exchange Server 2019 Cumulative Update 8 5001779 (Security Update) Critical Remote Code Execution Yes
Microsoft Exchange Server 2019 Cumulative Update 9 5001779 (Security Update) Critical Remote Code Execution Yes

Patches

1 patch
Article Type Restart
5001779 Security Update Yes

Exploits & PoC

Detection Rules

Detection available

Nuclei templates 1

CVE-2021-28481 Microsoft Exchange - Pre-Auth SSRF / ACL Bypass (ProxyNotFound) critical
nuclei -id CVE-2021-28481

Acknowledgments

National Security Agency
Microsoft Security Team

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