Home→Vulnerabilities→CVE-2021-34473
Critical Risk Active Exploitation

CVE-2021-34473

Microsoft Exchange Server Remote Code Execution Vulnerability

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Confirmed Active Exploitation

This vulnerability is listed in the CISA KEV Catalog. Federal agencies are mandated to patch immediately. Immediate remediation is required.

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Public Exploit Available

A Proof-of-Concept (PoC) or exploit code for this vulnerability is publicly available. This significantly increases the risk of exploitation.

Exploitation Probability (EPSS)

Critical Priority
94.19%

The Exploit Prediction Scoring System (EPSS) uses machine learning to estimate the probability that a vulnerability will be exploited in the wild within the next 30 days.

0% (Theoretical)100% (Certainty)

7-Day Exploitation Trend

Vulnerability Timeline

2 events
Jul 14, 2021
Vulnerability Disclosed
Published to component-level vulnerability database.
Feb 24, 2025
Last Updated
Record updated with new analysis or tags.

Threat Actor Attribution

PREMIUM INTEL
Associated Groups:Lazarus Group, APT28
Ransomware Campaigns:LockBit 3.0, BlackCat
IoCs (Indicators):14 IPs, 3 Hashes

Remediation & Mitigation

SOLUTION

Official patches and mitigation steps are available for this vulnerability.

# Update Command
apt-get update && apt-get upgrade -y specific-package
# Verify installation
dpkg -l | grep package-name

Affected Products

3 Total
microsoft/exchange_server2013
microsoft/exchange_server2016
microsoft/exchange_server2019

References

PoC Exploit
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlPacketstormsecurity
ExploitThird Party AdvisoryVDB Entry
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-34473Microsoft
PatchVendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-821/Zerodayinitiative
Third Party AdvisoryVDB Entry
http://packetstormsecurity.com/files/163895/Microsoft-Exchange-ProxyShell-Remote-Code-Execution.htmlPacketstormsecurity
ExploitThird Party AdvisoryVDB Entry

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Vulnerability Details

CVSS Base Score
9.1/ 10
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Published Date
Jul 14, 2021
Last Modified
Feb 24, 2025
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