What is the CVSS score of CVE-2021-40539?

CVE-2021-40539 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 99.0%.

Is there a public PoC exploit available for CVE-2021-40539?

Yes, a public proof-of-concept exploit is available for CVE-2021-40539. Prioritise patching immediately. EPSS: 99.0%.

Is there a patch available for CVE-2021-40539?

Yes, a patch is available for CVE-2021-40539. Update the affected software to the latest version immediately.

Zoho CVE-2021-40539

CRITICAL

Use of Incorrectly-Resolved Name or Reference (CWE-706)

2021-09-07 cve@mitre.org

Authentication Bypass RCE Zoho Manageengine Adselfservice Plus Zohocorp

9.8

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-706 ASVS 5.0 V15 - Secure Coding and Architecture Incorrectly specified target
Impact	CVSS score of 9.8 (CRITICAL). Attack characteristics: network attack vector, low complexity, no 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 critical-severity affected system.

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

Exploited in the wild (CISA KEV) Patch available 99.0% exploitation probability (EPSS)

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AnalysisAI

Zoho ManageEngine ADSelfService Plus version 6113 and prior is vulnerable to REST API authentication bypass with resultant remote code execution. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, 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

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified under CWE-706. Zoho ManageEngine ADSelfService Plus version 6113 and prior is vulnerable to REST API authentication bypass with resultant remote code execution. Affected products include: Zohocorp Manageengine Adselfservice Plus. Version information: version 6113.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL

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

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

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

Sep 07, 2021 - 17:15 nvd

CRITICAL 9.8

DescriptionNVD

Zoho ManageEngine ADSelfService Plus version 6113 and prior is vulnerable to REST API authentication bypass with resultant remote code execution.

Threat Intelligence Overview

EPSS Score

99.0%

Top 0% exploitable

Exploit

POC

Public exploit code exists

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

CISA KEV

EPSS POC (2)

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 CRITICAL

CISA KEV Yes

Public POC Yes

EPSS 99.0%

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

Immediate

Exploitation· derived

Active

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact· derived

High

Priority Score

233

Low Medium High Critical

KEV: +50

EPSS: +99

CVSS: +49

PoC: +20

Weaponized: +15

Threat intel: 0

Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

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)NVD

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:*:*:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:-:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6100:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6101:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6102:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6103:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6104:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6105:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6106:*:*:*:*:*:*

cpe:2.3:a:zohocorp:manageengine_adselfservice_plus:6.1:6113:*:*:*:*:*:*

More in Zoho

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PGSQL:SubmitQuery.do in ZOHO ManageEngine OpManager 11.6, 11.5, and earlier allows remote administrators to bypass SQL q

CVE-2014-6037 HIGH Act Now POC

7.5 Oct 26

Directory traversal vulnerability in the agentUpload servlet in ZOHO ManageEngine EventLog Analyzer 9.0 build 9002 and 8

CVE-2015-7387 HIGH Act Now POC

7.5 Sep 28

ZOHO ManageEngine EventLog Analyzer 10.6 build 10060 and earlier allows remote attackers to bypass intended restrictions

CVE-2016-6601 HIGH Act Now POC

7.5 Jan 23

Directory traversal vulnerability in the file download functionality in ZOHO WebNMS Framework 5.2 and 5.2 SP1 allows rem

CVE-2014-6034 MEDIUM This Month POC

5.0 Dec 04

Directory traversal vulnerability in the com.me.opmanager.extranet.remote.communication.fw.fe.FileCollector servlet in Z

CVE-2014-3996 HIGH Act Now POC

7.5 Dec 05

SQL injection vulnerability in the LinkViewFetchServlet servlet in ManageEngine Desktop Central (DC) and Desktop Central

CVE-2017-11512 HIGH Act Now POC

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The ManageEngine ServiceDesk 9.3.9328 is vulnerable to arbitrary file downloads due to improper restrictions of the path

Same weakness CWE-706 – Use of Incorrectly-Resolved Name or Reference

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CVE-2023-28643 HIGH POC

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CVE-2022-27778 HIGH POC

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CVE-2024-27295 HIGH POC

8.2

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CVE-2023-22515 CRITICAL POC

9.8

CVE-2012-4681 CRITICAL POC

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CVE-2024-0012 CRITICAL POC

9.3

References

Advisories & patches

PATCH https://www.manageengine.com/products/self-service-password/kb/how-to-fix-authentication-bypass-vulnerability-in-REST-API.html REF https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-40539 REF https://www.manageengine.com

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