CVE-2021-34473

CRITICALNVD 9.19.8▲Trending — 4 sources updated this weekExploited in the wild

9.1

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3: 9.1
EG Score: 9.8(medium)
EPSS: 99.9%
KEV: ⚠ Exploited

Published

July 14, 2021

Last Modified

October 29, 2025

Advisory Details (4)

Auto-updated Jun 2, 2026

⚠️ Active exploitation confirmed. Patch available. Sources: microsoft, cisa.

cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473

generic

ZDI-21-821 | Zero Day Initiative

https://www.zerodayinitiative.com/advisories/ZDI-21-821/

microsoft Patch Available

Security Update Guide - Microsoft Security Response Center

Security Update Guide - Microsoft Security Response Center. Patch available via Microsoft Security Update

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473

generic

Packet Storm

http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.html

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-918Server-Side Request Forgery (SSRF)

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Microsoft MSRCCVE-2021-344732021-07-13
Microsoft Exchange Server Remote Code Execution Vulnerability

Data Freshness Timeline

(refreshed 20× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-04 06:55 UTCEG score recompute
2026-06-04 06:55 UTCVendor advisory
2026-06-04 06:55 UTCGHSA enrichment
2026-06-04 02:59 UTCEG score recompute
2026-06-04 02:59 UTCVendor advisory
2026-06-04 02:59 UTCGHSA enrichment
2026-06-03 23:03 UTCEG score recompute
2026-06-03 23:03 UTCVendor advisory
2026-06-03 23:03 UTCGHSA enrichment
2026-06-03 19:09 UTCkev_newly_listed
2026-06-03 19:07 UTCEG score recompute
2026-06-03 19:07 UTCVendor advisory
2026-06-03 19:07 UTCGHSA enrichment
2026-06-03 15:11 UTCEG score recompute
2026-06-03 15:11 UTCVendor advisory
2026-06-03 15:11 UTCGHSA enrichment
2026-06-03 11:14 UTCEG score recompute
2026-06-03 11:14 UTCVendor advisory
2026-06-03 11:14 UTCGHSA enrichment
2026-06-03 07:18 UTCEG score recompute

Publicly available exploits

(10 references)

Working exploit code is in the public domain (2 Metasploit modules) (7 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

GitHub PoCipsBruno/CVE-2021-34473-NMAP-SCANNER
First seen Nov 16, 2022
A massive scanner for CVE-2021-34473 Microsoft Exchange Windows Vulnerability
Open source ↗
GitHub PoCkh4sh3i/ProxyShell
First seen Jun 29, 2022
CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability
Open source ↗
GitHub PoCje6k/CVE-2021-34473-Exchange-ProxyShell
First seen Nov 22, 2021
对Exchange Proxyshell 做了二次修改，精确的拆分、实现辅助性安全测试。
Open source ↗
GitHub PoChorizon3ai/proxyshell
First seen Sep 4, 2021
Proof of Concept for CVE-2021-34473, CVE-2021-34523, and CVE-2021-31207
Open source ↗
GitHub PoCp2-98/CVE-2021-34473
First seen Aug 16, 2021
CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability
Open source ↗
GitHub PoCRaouzRouik/CVE-2021-34473-scanner
First seen Aug 11, 2021
Scanner for CVE-2021-34473, ProxyShell, A Microsoft Exchange On-premise Vulnerability
Open source ↗
GitHub PoCcyberheartmi9/Proxyshell-Scanner
First seen Aug 10, 2021
nuclei scanner for proxyshell ( CVE-2021-34473 )
Open source ↗
Metasploitexploit/windows/http/exchange_proxyshell_rce✓ verified
First seen Aug 9, 2021
Exchange ProxyShell chain — combined with CVE-2021-34523 and CVE-2021-31207 for RCE.
Open source ↗
Metasploitexploit/windows/http/exchange_proxyshell_rce✓ verified
First seen Apr 6, 2021
Microsoft Exchange ProxyShell RCE
Open source ↗
Nucleihttp/cves/2021/CVE-2021-34473.yaml
First seen Jan 1, 2021
Exchange Server - Remote Code Execution
Open source ↗

Frequently asked(6)

What is CVE-2021-34473?

CVE-2021-34473 is a critical vulnerability published on July 14, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability

When was CVE-2021-34473 disclosed?

CVE-2021-34473 was first published in the National Vulnerability Database on July 14, 2021, with the most recent update on October 29, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-34473 actively exploited?

Yes. CISA added CVE-2021-34473 to the Known Exploited Vulnerabilities catalog on November 3, 2021, affecting Microsoft Exchange Server. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.

What is the CVSS score of CVE-2021-34473?

CVE-2021-34473 has a CVSS v3 base score of 9.1 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.8.

Which products are affected by CVE-2021-34473?

CVE-2021-34473 affects Microsoft Exchange Server. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.

How do I remediate CVE-2021-34473?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-34473, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-34473

Explore →

Is Your Infrastructure Affected by CVE-2021-34473?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs

CVE-2021-34473

Published

Last Modified

Advisory Details (4)

Known Exploited Vulnerabilities Catalog | CISA

ZDI-21-821 | Zero Day Initiative

Security Update Guide - Microsoft Security Response Center

Packet Storm

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-34473?

Same vendor

Same CWE

CVE-2021-34473

📅 Published

🔄 Last Modified

📋 Advisory Details (4)

Known Exploited Vulnerabilities Catalog | CISA

ZDI-21-821 | Zero Day Initiative

Security Update Guide - Microsoft Security Response Center

Packet Storm

Weakness Classification(1)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

❓ Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-34473?

🔗 Related CVEs(same vendor + same CWE)

Same vendor

Same CWE

Published

Last Modified

Advisory Details (4)

Frequently asked(6)

Related CVEs(same vendor + same CWE)