CVE-2021-28480 — Microsoft Exchange Server Remote Code Execution Vulnerability

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 0.71425 — 0.9936 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

0.71425

probability of exploitation in the next 30 days

0.9936 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

2 public PoCs

Unverified third-party code

Public proof-of-concept repositories aggregated from PoC-in-GitHub. They are not reviewed and may be incomplete, non-functional, or malicious — inspect the code before running anything.

Repository	Stars	Published	Description
ZephrFish/CVE-2021-28480_HoneyPoC3	10	2021-04-21	DO NOT RUN THIS.
Threonic/CVE-2021-28480	0	2022-03-30

Detection Rules

Detection available

Community detection & vulnerability-scanning rules aggregated from Sigma and Nuclei templates. Validate and tune to your environment before deploying.

Sigma rules 1

Exchange Exploitation CVE-2021-28480 critical

Nuclei templates 1

CVE-2021-28480 Microsoft Exchange - Pre-Auth SSRF / ACL Bypass (ProxyNotFound) critical

nuclei -id CVE-2021-28480

Acknowledgments

National Security Agency
Microsoft Security Team

References

MSRC Advisory MITRE NVD