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/E:U/RL:O/RC:C
- 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
Weaponization
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.
No public GitHub repositories referencing CVE-2021-34473 were found at last check. Absence here is not proof no exploit exists - see the references below for vendor advisories and write-ups.
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.
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.
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