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Critical Zoho Zero-Day Vulnerability

September 9, 2021 | 1 MIN READ

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On September 8th, 2021, Zoho announced a critical zero-day authentication bypass vulnerability impacting the ManageEngine ADSelfService Plus solution. Attacks exploiting this vulnerability are ongoing; organizations are strongly recommended to apply the available security patches as soon as possible.

The vulnerability is tracked as CVE-2021-40539; it is an authentication bypass vulnerability that allows for Remote Code Execution (RCE). According to the Cybersecurity and Infrastructure Agency (CISA), an unauthenticated remote actor may exploit this vulnerability to take control of affected systems. As attacks are ongoing and alternative mitigations are not available, it is critical that impacted organizations apply the Zoho provided security patches as soon as possible.

What we’re doing about it

What you should do about it

Additional information

CVE-2021-40539 impacts all ManageEngine ADSelfService Plus builds versions 6113 and below.

Information relating to this vulnerability and real-world attacks is still limited. Public sources have stated that attacks exploiting CVE-2021-40539 have been ongoing for at least a week prior to patch release. These attacks are believed to be targeted in nature. No Proof-of-Concept exploit code is known to exist at this time. As the vulnerability is now public knowledge, it is likely that additional threat actor groups will develop exploits in the near future, leading to widespread exploitation.


[1] https://www.manageengine.com/products/self-service-password/kb/how-to-fix-authentication-bypass-vulnerability-in-REST-API.html
[2] https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-40539
[3] https://us-cert.cisa.gov/ncas/current-activity/2021/09/07/zoho-releases-security-update-adselfservice-plus
[4] https://help.zoho.com/portal/en/kb/vault/integration-guide/articles/password-manager-syslog-siem-integration#Integration_with_Loggly
[5] https://therecord.media/cisa-warns-of-zoho-server-zero-day-exploited-in-the-wild/
[6] https://twitter.com/voodoodahl1/status/1435673340539281410

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