Attacker Value
Very High
(2 users assessed)
Exploitability
Moderate
(2 users assessed)
User Interaction
None
Privileges Required
None
Attack Vector
Network
4

CVE-2021-34473

Disclosure Date: July 14, 2021 •
CVE-2021-34473 CVSS v3 Base Score: 9.1
Exploited in the Wild
Reported by gwillcox-r7 and 2 more...
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Add MITRE ATT&CK tactics and techniques that apply to this CVE.
Initial Access
Techniques
Validation
Validated

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

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2
Ratings
  • Attacker Value
    Very High
  • Exploitability
    Medium
Common in enterpriseGives privileged accessVulnerable in default configuration
Technical Analysis

From https://blog.talosintelligence.com/2021/07/microsoft-patch-tuesday-for-july-2021.html there was a note that this vulnerability seems to have been used in some Exchange Server APT attacks detailed at https://blog.talosintelligence.com/2021/03/hafnium-update.html however it wasn’t disclosed that this vulnerability was patched despite being patched back in April 2021. Since this was under active exploitation it is recommended to patch this vulnerability if you haven’t applied April 2021’s patch updates already.

Successful exploitation will result in RCE on affected Exchange Servers, and requires no prior user privileges, so patch this soon!

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1
Ratings
Observed in ransomware attacks
Technical Analysis

CISA released an updated advisory on the BianLian ransomware group including the vulnerabilities the group is using to gain initial access towards victims.

https://www.cisa.gov/sites/default/files/2024-11/aa23-136a-joint-csa-stopransomware-bianlian-ransomware-group.pdf

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CVSS V3 Severity and Metrics
Base Score:
9.1 Critical
Impact Score:
5.2
Exploitability Score:
3.9
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector (AV):
Network
Attack Complexity (AC):
Low
Privileges Required (PR):
None
User Interaction (UI):
None
Scope (S):
Unchanged
Confidentiality (C):
High
Integrity (I):
High
Availability (A):
None

General Information

Offensive Application
Unknown
Utility Class
Unknown
Ports
Unknown
OS
Unknown
Vulnerable Versions
Microsoft Exchange Server 2013 Cumulative Update 23 15.00.1497.015
Microsoft Exchange Server 2019 Cumulative Update 9 15.02.0858.010
Microsoft Exchange Server 2016 Cumulative Update 20 15.01.2242.008
Microsoft Exchange Server 2016 Cumulative Update 19 15.01.2176.012
Microsoft Exchange Server 2019 Cumulative Update 8 15.02.0792.013
Prerequisites
Unknown
Discovered By
Unknown
PoC Author
Unknown
Metasploit Module
Unknown
Reporter
Unknown

Vendors

  • microsoft

Products

  • exchange server 2013,
  • exchange server 2016,
  • exchange server 2019

Exploited in the Wild

Reported by:
Technical Analysis