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Fencer Intel
high 7.5

CVE-2021-34453 json

Microsoft Exchange Server Denial of Service Vulnerability

published 5y ago modified 4mo ago also EUVD-2021-21108

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
2.8%
EPSS 2.8% chance of exploitation in 30 days, percentile 86%
public exploits
0
none known

Summary

Microsoft Exchange Server Denial of Service Vulnerability

Patch / fix

  • Microsoft Microsoft Exchange Server 2019 Cumulative Update 11 15.02.0986.009
  • Microsoft Microsoft Exchange Server 2019 Cumulative Update 10 15.02.0922.014
  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 21 15.01.2308.015
  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 22 15.01.2375.012

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2y ago

Exploit prediction

2.83% chance of exploitation in the next 30 days, higher than 86% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • Microsoft Microsoft Exchange Server 2019 Cumulative Update 11
  • Microsoft Microsoft Exchange Server 2019 Cumulative Update 10
  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 21
  • Microsoft Microsoft Exchange Server 2016 Cumulative Update 22

Classification

Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.