CVE-2021-40539
CVE-2021-40539 is a security flaw in Zoho ManageEngine, Zoho’s IT management software. Attackers can run their own code on Zoho ManageEngine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021, and says ransomware gangs have used it.[1]
Zoho ManageEngine is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Zoho has published a fix or advice.
Description
CISA calls it an aDSelfService plus authentication bypass in Zoho ManageEngine. In its words: “Zoho ManageEngine ADSelfService Plus contains an authentication bypass vulnerability affecting the REST API URLs which allow for remote code execution.”[1]
The underlying weakness is CWE-55, in MITRE’s list of common software weaknesses.[2]
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Zoho’s advisory has them[3]. CISA names the product as Zoho ManageEngine.
Most families won’t have Zoho ManageEngine; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 57 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 17 Nov 2021 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Zoho has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Zoho ManageEngine is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 17 Nov 2021 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 99%.[4] |
See also
Other Zoho ManageEngine flaws
- CVE-2022-28810: aDSelfService plus remote code execution ·
- CVE-2022-47966: multiple products remote code execution ·
- CVE-2022-35405: multiple products remote code execution ·
- CVE-2020-10189: desktop central file upload ·
- CVE-2019-8394: serviceDesk plus (SDP) file upload ·
Other Zoho flaws
- CVE-2021-44515, Zoho Desktop Central: authentication bypass ·
- CVE-2021-44077, Zoho ManageEngine ServiceDesk Plus (SDP) / SupportCenter Plus: manageEngine serviceDesk plus remote code execution ·
- CVE-2021-37415, Zoho ManageEngine ServiceDesk Plus (SDP): manageEngine serviceDesk authentication bypass ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
- CVE-2021-38649, Microsoft Open Management Infrastructure (OMI): privilege escalation ·
Every Zoho flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Zoho ManageEngine ADSelfService Plus Authentication Bypass Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-40539 Detail”. National Vulnerability Database, published 7 Sep 2021.
- ^ Zoho. Advisories and fixes: manageengine.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.990, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2021-40539”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.