CISA warns of Zoho server zero

Zoho ManageEngine Desktop Central contains a file upload vulnerability (CWE-502, deserialization of untrusted data) that can be exploited without authentication. A remote attacker sends crafted upload requests to the affected application, which accepts and processes the uploaded content without any credentials, resulting in execution of attacker-controlled code. Successful exploitation yields remote code execution on the server hosting Desktop Central, giving the attacker a foothold on an endpoint-management system that typically has broad reach into a corporate network. Any organization running the affected Zoho ManageEngine product is exposed, and exploitability does not depend on user interaction or credentials. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating known exploitation in the wild, and EPSS assigns a 99.9% probability of exploitation within 30 days; specific exploited versions are not stated in the available data.

Do: Apply updates per Zoho/ManageEngine vendor instructions immediately, as the CISA KEV required action specifies. Restrict internet exposure of the Desktop Central server and audit it for signs of compromise (unexpected processes, webshells, outbound connections) since unauthenticated RCE has been exploited in the wild. Check that any exposed instances are patched before treating network access as safe.

CVE-2021-40539 is a critical (CVSS 9.8) authentication bypass in the REST API of Zoho ManageEngine ADSelfService Plus, caused by use of an incorrectly resolved name or reference (CWE-706). An unauthenticated, network-adjacent or internet-reachable attacker sends specially crafted requests to the product's REST API, bypassing authentication, and can chain the bypass to full remote code execution with no privileges or user interaction required. Successful exploitation yields complete compromise of the self-service portal server (high impact to confidentiality, integrity and availability); public reporting and vendor notes document attackers dropping malicious code and web shells onto vulnerable servers. Any organization running ManageEngine ADSelfService Plus build 6113 or earlier is affected, which typically means enterprise Microsoft Active Directory environments running this widely deployed self-service password/SSO portal. Exploitation is confirmed in the wild: the flaw was added to CISA KEV on 2021-11-03 with known ransomware use, EPSS puts the 30-day exploitation probability at 99% (100th percentile), Microsoft warned that Chinese threat actors were actively exploiting it, a public proof-of-concept is available, and it ranked among CISA's most routinely exploited vulnerabilities.

Do: Immediately upgrade ManageEngine ADSelfService Plus to a fixed build newer than 6113 per the vendor's update instructions, as required by CISA. Because exploitation predates patching and the flaw has been used to drop malicious code, check ADSelfService Plus servers for web shells, unexpected scheduled tasks, and unexplained accounts/processes, and hunt for indicators from the published analyses. Where possible, restrict internet exposure of the ADSelfService Plus REST API while patching, prioritized for externally reachable instances.