Is CVE-2021-40539 in the CISA KEV catalog?

Yes. CVE-2021-40539 is on the CISA Known Exploited Vulnerabilities list, added 2021-11-03, and has known ransomware campaign use.

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

CVE-2021-40539 has a CVSS v3 base score of 9.8 (CRITICAL).

What is the EPSS score for CVE-2021-40539?

CVE-2021-40539 has an EPSS score of 98.96% (100th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-40539?

Upgrade manageengine adselfservice plus to 6.1 or later.

CVE & CISA-KEV Catalog

CVE-2021-40539

CRITICALCISA KEVEPSS 100th pctl

9.8

CVSS v3

NVD

Description

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

CWE-706

How to fix

Remediation Available

manageengine adselfservice plusNVD

Affected:< 6.1Fixed in:6.1CVE-2021-40539derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Exploit Intelligence

98.96%probability of exploitation in 30 days

100thpercentile

Very high risk: more likely to be exploited than 100% of all known CVEs.

Known Exploited Vulnerability (CISA KEV)

Zoho ManageEngine ADSelfService Plus Authentication Bypass Vulnerability

Zoho ManageEngine ADSelfService Plus contains an authentication bypass vulnerability affecting the REST API URLs which allow for remote code execution.

Apply updates per vendor instructions.

Remediation due: 2021-11-17

Associated with ransomware campaigns

References

Patch1

manageengine.com

Exploit1

packetstormsecurity.com

Government Resource1

cisa.gov

Product1

manageengine.com

Related Vulnerabilities

Other CWE-706 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-24813	Critical	9.8	100%	KEV	Fix
CVE-2020-15505	Critical	9.8	100%	KEV	Fix
CVE-2024-27292	High	7.5	69%	-	Fix
CVE-2021-40856	High	7.5	51%	-	-
CVE-2021-24122	Medium	5.9	23%	-	Fix
CVE-2019-0220	Medium	5.3	18%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-05.