Microsoft Exchange Server Remote Code Execution Vulnerability
Microsoft — Microsoft Exchange Server 2013 Cumulative Update 23
Microsoft Exchange Server Remote Code Execution Vulnerability
9.1
100.0%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- Published
- Jul 14, 2021
- Modified
- Aug 10, 2026
- Added to KEV
- Nov 3, 2021
- Federal patch due
- Nov 17, 2021
CISA required action
Apply updates per vendor instructions.
Weakness classification
Affected packages
Proof-of-concept & exploitation references
8 foundWeaponization
Public repositories whose name or description references CVE-2021-34473, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit — cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
- hosch3n/ProxyVulns★ 176
[ProxyLogon] CVE-2021-26855 & CVE-2021-27065 Fixed RawIdentity Bug Exploit. [ProxyOracle] CVE-2021-31195 & CVE-2021-31196 Exploit Chains. [ProxyShell] CVE-2021-34473 & CVE-2021-34523 & CVE-2021-31207 Exploit Chains.
updated Oct 13, 2026
- psc4re/NSE-scripts★ 162
NSE scripts to detect CVE-2020-1350 SIGRED and CVE-2020-0796 SMBGHOST, CVE-2021-21972, proxyshell, CVE-2021-34473
updated Aug 15, 2026
- horizon3ai/proxyshell★ 121
Proof of Concept for CVE-2021-34473, CVE-2021-34523, and CVE-2021-31207
updated Sep 19, 2026
- cyberheartmi9/Proxyshell-Scanner★ 46
nuclei scanner for proxyshell ( CVE-2021-34473 )
updated May 18, 2026
- kh4sh3i/ProxyShell★ 43
CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability
updated Oct 6, 2026
- p2-98/CVE-2021-34473★ 30
CVE-2021-34473 Microsoft Exchange Server Remote Code Execution Vulnerability
updated Feb 27, 2025
- je6k/CVE-2021-34473-Exchange-ProxyShell★ 16
对Exchange Proxyshell 做了二次修改，精确的拆分、实现辅助性安全测试。
updated Sep 19, 2026
- mithridates1313/ProxyShell_POC★ 16
POC for scanning ProxyShell(CVE-2021-34523,CVE-2021-34473,CVE-2021-31207)
updated Jan 13, 2026
References
How this class of flaw gets exploited
Frequently asked questions
What is CVE-2021-34473?
Microsoft Exchange Server Remote Code Execution Vulnerability
How severe is CVE-2021-34473?
CVE-2021-34473 has a CVSS base score of 9.1 out of 10 (CVSS 3.1).
Is CVE-2021-34473 actively exploited in the wild?
Yes. CVE-2021-34473 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Nov 3, 2021, meaning CISA has confirmed evidence of active exploitation. It is also flagged as used in ransomware campaigns.
What is the EPSS score for CVE-2021-34473?
100.0% - meaning FIRST.org's EPSS model estimates a 100.0% probability this vulnerability will be exploited in the wild within 30 days (100% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2021-34473?
Yes - a public Nuclei template referencing CVE-2021-34473 exist in public repositories we checked. We also found 8 public GitHub repositories referencing this CVE.
What type of vulnerability is CVE-2021-34473?
CVE-2021-34473 is classified under CWE-918 (CWE-918 Server-Side Request Forgery (SSRF)).
Cross-checked against
Impactr finds and proves whether CVE-2021-34473 — or flaws like it — are actually reachable in your own web apps and APIs, with a reproducible exploit as evidence.