CVE-2021-34473

CRITICAL
2021-07-14 [email protected]
9.1
CVSS 3.1
Share

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

5
Analysis Generated
Mar 26, 2026 - 11:19 vuln.today
Added to CISA KEV
Oct 29, 2025 - 16:46 cisa
CISA KEV
PoC Detected
Oct 29, 2025 - 16:46 vuln.today
Public exploit code
Patch Released
Oct 29, 2025 - 16:46 nvd
Patch available
CVE Published
Jul 14, 2021 - 18:15 nvd
CRITICAL 9.1

Description

Microsoft Exchange Server Remote Code Execution Vulnerability

Analysis

Microsoft Exchange Server contains a pre-authentication SSRF vulnerability known as 'ProxyShell' that allows unauthenticated attackers to access Exchange backend services and achieve remote code execution when chained with CVE-2021-34523 and CVE-2021-31207.

Technical Context

The CWE-918 SSRF exploits the same Exchange Client Access architecture as ProxyLogon but through a different code path. Attackers abuse the autodiscover normalization to access the Exchange PowerShell backend without authentication, enabling mailbox access and command execution.

Affected Products

['Microsoft Exchange Server 2013', 'Microsoft Exchange Server 2016', 'Microsoft Exchange Server 2019']

Remediation

Apply all Exchange security updates. ProxyShell patches were included in April and May 2021 cumulative updates. Scan for web shells. Consider migrating to Exchange Online to reduce on-premises attack surface.

Priority Score

220
Low Medium High Critical
KEV: +50
EPSS: +94.2
CVSS: +46
POC: +20

Share

CVE-2021-34473 vulnerability details – vuln.today
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy