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CVE-2021-34473

CRITICAL
Server-Side Request Forgery (SSRF) (CWE-918)
2021-07-14 secure@microsoft.com
9.1
CVSS 3.1
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CVSS VectorNVD

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

DescriptionNVD

Microsoft Exchange Server Remote Code Execution Vulnerability

AnalysisAI

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 ContextAI

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 ProductsAI

Microsoft Exchange Server 2013 Microsoft Exchange Server 2016 Microsoft Exchange Server 2019

RemediationAI

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.

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CVE-2021-34473 vulnerability details – vuln.today
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