CVE-2021-40539: Zoho ManageEngine ADSelfService Plus Authentication Bypass Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, 57 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 99%
EPSS score, percentile 99.9 of all scored records
- How severe?
- 9.8 Critical
CVSS v3.1 base score, from CISA's enrichment of the record
- What should I do?
CISA deadline 17 Nov 2021. Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Not stated. The CVE record gives vendor and product as “n/a” and the version as “unspecified”.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: 17 November 2021.
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
Affected products and versions
The CVE record does not name affected products or versions: vendor and product are “n/a” and the version is “unspecified”.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
Zoho ManageEngine ADSelfService Plus contains an authentication bypass vulnerability affecting the REST API URLs which allow for remote code execution.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2021-40539 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 17 Nov 2021.
- The CVE record was published on 7 Sep 2021, 57 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), taken from CISA's enrichment of the record.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 99% (percentile 99.9), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
Description
Zoho ManageEngine ADSelfService Plus version 6113 and prior is vulnerable to REST API authentication bypass with resultant remote code execution.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 7 Sep 2021 | CVE record published |
| 3 Nov 2021 | Added to CISA KEV |
| 17 Nov 2021 | CISA due date for the required action |
| 21 Oct 2025 | CVE record last updated |
References
More exploited Zoho vulnerabilities
- CVE-2022-28810: Zoho ManageEngine ADSelfService Plus Remote Code Execution Vulnerability
- CVE-2022-47966: Zoho ManageEngine Multiple Products Remote Code Execution Vulnerability
- CVE-2022-35405: Zoho ManageEngine Multiple Products Remote Code Execution Vulnerability
- CVE-2021-44515: Zoho Desktop Central Authentication Bypass Vulnerability
- CVE-2021-37415: Zoho ManageEngine ServiceDesk Authentication Bypass Vulnerability
- CVE-2021-44077: Zoho ManageEngine ServiceDesk Plus Remote Code Execution Vulnerability