Trend Micro Apex One and OfficeScan Arbitrary File Upload Vulnerability (CVE-2021-36741) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTTrend Micro Apex One, Apex One as a Service, OfficeScan XG, and Worry-Free Business Security 10.0 SP1
An authenticated attacker with management console access can exploit improper input validation to upload arbitrary files, potentially leading to Remote Code Execution (RCE)
Apply the latest official security patches and service packs immediately, and restrict access to the management console
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators should immediately download and apply the latest Critical Patches (CP) or Service Packs from the Trend Micro Support Portal.
# Verify the currently installed version of Trend Micro Apex One via PowerShell
Get-WmiObject -Class Win32_Product | Where-Object { $_.Name -like '*Trend Micro Apex One*' } | Select-Object Name, Version2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to the management console port (typically port 4343) to trusted administrative IP addresses only.
# Example Nginx configuration to restrict access to the management console
server {
listen 80;
server_name apex-console.local;
location / {
allow 10.0.0.0/8; # Allow internal admin network
deny all; # Block all other traffic
proxy_pass https://127.0.0.1:4343;
}
}3. Log Audit & IoC Verification Commands
Audit the web directories and logs for any unauthorized file creations or suspicious web shell uploads.
# Search for recently modified or created script files in the Trend Micro installation directory (Linux/Unix-like environments if applicable)
find /opt/TrendMicro/ -type f \( -name "*.jsp" -o -name "*.php" -o -name "*.sh" \) -mtime -30 -lsBlock Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-36741) is an improper input validation flaw (CWE-434) residing in the management console of Trend Micro endpoint security products. The root cause lies in the insufficient validation of file extensions, paths, and execution permissions during file upload operations via the administrative interface. If an attacker gains access to the management console, they can bypass these weak validation routines to upload arbitrary files to sensitive directories.
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, an attacker must first obtain valid credentials to log into the product's management console (e.g., through credential stuffing, phishing, or default configurations). Once authenticated, the attacker sends a crafted HTTP POST request to the file upload endpoint. By manipulating the filename or path parameters (potentially using directory traversal sequences), the attacker forces the server to write an executable payload (such as a web shell) into a web-accessible directory. Accessing the uploaded file via its URL executes the payload under the context of the web server process.
3. Infrastructure & Business Impact
As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, the risk is critical. Compromising the central endpoint security management server allows threat actors to distribute malicious policies, disable endpoint protection across the enterprise, or deploy ransomware. This can lead to complete infrastructure compromise and severe business disruption.
Official Vendor Advisories & References
An improper input validation vulnerability in Trend Micro Apex One, Apex One as a Service, OfficeScan XG, and Worry-Free Business Security 10.0 SP1 allows a remote attached to upload arbitrary files on affected installations. Please note: an attacker must first obtain the ability to logon to the product�s management console in order to exploit this vulnerability.
Frequently Asked SecOps Questions (CVE-2021-36741)
FAQQ1. How critical is CVE-2021-36741 and is it actively exploited in the wild?
CVE-2021-36741 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 5.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-36741?
Primary impacted vendors include trendmicro across apex_one, apex_one_as_a_service, officescan, worry-free_business_security. Scope summary: Trend Micro Apex One (On-Premise & SaaS), OfficeScan XG, and Worry-Free Business Security 10.0 SP1
Q3. What temporary mitigations or workarounds exist for CVE-2021-36741 before patching?
[Mitigation] Apply the latest official security patches and service packs immediately, and restrict access to the management console Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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