Summary
generated automatically from NVD dataCVE-2021-34473 affects Microsoft Exchange Server (2013, 2016 and 2019) and is described as a remote code execution vulnerability, classified under CWE-918 (server-side request forgery). It can be reached over the network without privileges or user interaction, and the vector rates confidentiality and integrity impact as high. It carries a CVSS v3.1 score of 9.1 (CRITICAL). CISA lists it in its KEV catalog, added 2021-11-03, with known use in ransomware campaigns.
NVD description
Microsoft Exchange Server Remote Code Execution Vulnerability
⚠️ Actively exploited — CISA KEV
This CVE was added to CISA's Known Exploited Vulnerabilities catalog on 2021-11-03. It is confirmed exploited in the wild and must be patched as a priority.
Remediation deadline (US federal agencies): 2021-11-17
Used in known ransomware campaigns.
EPSS · FIRST.org
100.0%probability of exploitation in the next 30 days
Higher than 99% of scored CVEs
EPSS (Exploit Prediction Scoring System) estimates, from observed exploitation activity, how likely a CVE is to be exploited in the next 30 days. It complements CVSS, which measures severity, not likelihood. Score of 2026-10-16, recomputed daily by FIRST.org.
In-depth analysis on cveo.tech
We've published a detailed analysis of this CVE — exploitation, IOCs and mitigation.
CVSS v3.1 Score
Information
- Published
- 14 juil. 2021
- Updated
- 10 août 2026
- Status
- Analyzed
- Source
- secure@microsoft.com
Affected products
Weaknesses (CWE)
References (5)
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34473PatchVendor Advisory
- http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlExploitThird Party AdvisoryVDB Entry
- https://www.zerodayinitiative.com/advisories/ZDI-21-821/Third Party AdvisoryVDB Entry
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-34473US Government Resource
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