What is the CVSS score of CVE-2021-42321?

CVE-2021-42321 has a CVSS 3.1 base score of 8.8 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 90.4%.

Is there a public PoC exploit available for CVE-2021-42321?

Yes, a public proof-of-concept exploit is available for CVE-2021-42321. Prioritise patching immediately. EPSS: 90.4%.

Is there a patch available for CVE-2021-42321?

Yes, a patch is available for CVE-2021-42321. Update the affected software to the latest version immediately.

Exchange Server CVE-2021-42321

HIGH

2021-11-10 secure@microsoft.com

RCE Microsoft Exchange Server

8.8

CVSS 3.1 · Vendor: microsoft

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Vulnerability Assessment

Impact	CVSS score of 8.8 (HIGH). Attack characteristics: network attack vector, low complexity, low privileges required, no user interaction not required. Public proof-of-concept exploit code is available.
Exploit ScenarioDerived	This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the high-severity affected system.

Act Now Prioritize within 24-48h. Why: In CISA KEV with patch available.

Exploited in the wild (CISA KEV) Patch available 90.4% exploitation probability (EPSS)

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AnalysisAI

Microsoft Exchange Server Remote Code Execution Vulnerability. Rated high severity (CVSS 8.8), this vulnerability is remotely exploitable, low attack complexity. Public exploit code available.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

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Technical ContextAI · show details

Microsoft Exchange Server Remote Code Execution Vulnerability Affected products include: Microsoft Exchange Server.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (microsoft) PRIMARY 8.8 HIGH

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

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

CVSS VectorVendor: microsoft

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Added to CISA KEV

Jul 14, 2026 - 04:22 CISA

CVE Published

Nov 10, 2021 - 01:19 cve.org

HIGH 8.8

DescriptionCVE.org

Microsoft Exchange Server Remote Code Execution Vulnerability

Threat Intelligence Overview

Threat Score

7.5/10

Composite threat intelligence

EPSS Score

90.4%

Top 0% exploitable

Exploit

POC

Public exploit code exists

Data Quality

5 sources

Confidence: Medium

NVD

CVE.org

CISA KEV

EPSS POC (1)

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV Yes

Public POC Yes

EPSS 90.4%

Patch available Yes

Active threat Yes

Deciding rule

In CISA KEV with patch available

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Active

System Exposure· derived

Open

Automatable· derived

Human Impact· derived

High

Priority Score

219

Low Medium High Critical

KEV: +50

EPSS: +90

CVSS: +44

PoC: +20

Weaponized: +15

Threat intel: 0

Gov advisory: 0

Attack Technique

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)CVE.org

cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_21:*:*:*:*:*:*

cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_22:*:*:*:*:*:*

cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_10:*:*:*:*:*:*

cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_11:*:*:*:*:*:*

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References

Advisories & patches

PATCH https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42321 REF https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42321 REF https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-42321

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GitHub PoC

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