What is CVE-2021-40539?

CVE-2021-40539 is a critical-severity vulnerability in Zohocorp Manageengine Adselfservice Plus, classified under Use of Incorrectly-Resolved Name or Reference. CVSS score: 9.8/10. Published 2021-09-07.

How severe is CVE-2021-40539?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-40539 known to be exploited?

Yes. CVE-2021-40539 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 33 public proof-of-concept repositories are indexed.

Vulnerability in Zohocorp Manageengine Adselfservice Plus

CVE-2021-40539

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

Published 2021-09-07 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.990 (99.9th percentile), scored 2026-10-17.

Very high probability of exploitation in the next 30 days — among the top 0.1% most-likely-to-be-exploited CVEs. 100th percentile — 99.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.990 · newest: 0.990 · change: 0.000

Affected products

Zohocorp Manageengine Adselfservice Plus — versions 6.1

Weakness classification (CWE)

CWE-706 — Use of Incorrectly-Resolved Name or Reference

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Known ransomware campaign use: yes.

Public proof-of-concept exploits

References

www.manageengine.com (Product)
www.manageengine.com/products/self-service-password/kb/how-to-fix-authenticatio… (Patch, Vendor Advisory)
packetstormsecurity.com/files/165085/ManageEngine-ADSelfService-Plus-Authentica… (Exploit, VDB Entry, Third Party Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-40539?: CVE-2021-40539 is a critical-severity vulnerability in Zohocorp Manageengine Adselfservice Plus, classified under Use of Incorrectly-Resolved Name or Reference. CVSS score: 9.8/10. Published 2021-09-07.
How severe is CVE-2021-40539?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-40539 known to be exploited?: Yes. CVE-2021-40539 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 33 public proof-of-concept repositories are indexed.