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Actively exploitedKnown ransomware use

CVE-2021-40539 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.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 3 Nov 2021.
  • CISA lists it as known to be used in ransomware campaigns.
  • Rated Critical severity (CVSS 9.8, scored by CISA).
  • It has been in the catalogue for 1,829 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

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

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Zoho ManageEngine. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 17 Nov 2021 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Zoho Flaws

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CVE-2022-28810Zoho ManageEngine ADSelfService Plus Remote Code Execution VulnerabilityAdded 7 Mar 2023CVE-2022-47966 · RansomwareZoho ManageEngine Multiple Products Remote Code Execution VulnerabilityAdded 23 Jan 2023CVE-2022-35405Zoho ManageEngine Multiple Products Remote Code Execution VulnerabilityAdded 22 Sep 2022CVE-2021-44515Zoho Desktop Central Authentication Bypass VulnerabilityAdded 10 Dec 2021CVE-2021-37415Zoho ManageEngine ServiceDesk Authentication Bypass VulnerabilityAdded 1 Dec 2021CVE-2021-44077Zoho ManageEngine ServiceDesk Plus Remote Code Execution VulnerabilityAdded 1 Dec 2021

All 9 exploited Zoho vulnerabilities

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2021-40539
  3. CVE record: CVE-2021-40539
  4. FIRST EPSS
  5. manageengine.com
  6. manageengine.com/products/self-service-password/kb/how-to-fix-authentication-bypass-vulnerability-in
  7. packetstormsecurity.com/files/165085/ManageEngine-ADSelfService-Plus-Authentication-Bypass-Code-Exec