CVE-2021-42104 – This vulnerability allows a local attacker with... (How to Fix)

Q: What is the severity of CVE-2021-42104?

CVE-2021-42104 has a CVSS score of 7.8 (HIGH). This vulnerability allows a local attacker with low-privileged code execution on affected Trend Micro security products to escalate privileges to higher system levels. It affects Trend Micro Apex One, Apex One as a Service, Worry-Free Business Security 10.0 SP1, and Worry-Free Business Security Services. Attackers must already have some foothold on the system to exploit this privilege escalation flaw.

📋 TL;DR

This vulnerability allows a local attacker with low-privileged code execution on affected Trend Micro security products to escalate privileges to higher system levels. It affects Trend Micro Apex One, Apex One as a Service, Worry-Free Business Security 10.0 SP1, and Worry-Free Business Security Services. Attackers must already have some foothold on the system to exploit this privilege escalation flaw.

💻 Affected Systems

Products:

Trend Micro Apex One
Trend Micro Apex One as a Service
Trend Micro Worry-Free Business Security 10.0 SP1
Trend Micro Worry-Free Business Security Services

Versions: Specific vulnerable versions not explicitly stated in references; affected versions prior to patches released in October 2021

Operating Systems: Windows

Default Config Vulnerable: ⚠️ Yes

Notes: Affects both on-premises and cloud/SaaS versions. Requires local access with low privileges to exploit.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise with administrative/root privileges, enabling installation of persistent malware, data theft, lateral movement, and disabling of security controls.

🟠

Likely Case

Local privilege escalation allowing attackers to bypass security restrictions, access sensitive data, and maintain persistence on compromised systems.

🟢

If Mitigated

Limited impact due to proper access controls, least privilege principles, and network segmentation preventing initial low-privileged access.

🌐 Internet-Facing: LOW - This is a local privilege escalation requiring existing low-privileged access, not directly exploitable from the internet.

🏢 Internal Only: HIGH - Once an attacker gains initial access to a system (via phishing, malware, etc.), this vulnerability enables significant privilege escalation within the internal network.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires existing low-privileged access. Similar vulnerabilities (CVE-2021-42105, 42106, 42107) suggest pattern of privilege management issues in Trend Micro products.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patches released in October 2021; specific version numbers in vendor advisories

Vendor Advisory: https://success.trendmicro.com/solution/000289229

Restart Required: Yes

Instructions:

1. Review Trend Micro advisories 000289229 and 000289230. 2. Download and apply the latest security updates from Trend Micro. 3. Restart affected systems. 4. Verify patch installation through product console.

🔧 Temporary Workarounds

Restrict local access

windows

Limit user accounts with local login privileges to reduce attack surface for initial low-privileged access

Implement application whitelisting

windows

Use AppLocker or similar to prevent unauthorized low-privileged code execution

🧯 If You Can't Patch

Implement strict least privilege principles for all user accounts
Segment networks to limit lateral movement and contain potential privilege escalation

🔍 How to Verify

Check if Vulnerable:

Check Trend Micro product version against patched versions in advisories 000289229/000289230

Check Version:

Check through Trend Micro product management console or review installed version in Windows Programs and Features

Verify Fix Applied:

Verify product version is updated to post-October 2021 patches through Trend Micro console

📡 Detection & Monitoring

Log Indicators:

Unusual privilege escalation events in Windows Security logs
Trend Micro service account performing unexpected actions
Process creation from Trend Micro directories with elevated privileges

Network Indicators:

Lateral movement from systems running vulnerable Trend Micro products
Unexpected outbound connections from Trend Micro-managed systems

SIEM Query:

EventID=4688 AND (ProcessName LIKE '%trend%' OR ParentProcessName LIKE '%trend%') AND NewIntegrityLevel>Medium

📊 Metadata

CVE ID: CVE-2021-42104

CVSS v3 Score: 7.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-269

Published: October 21, 2021

Last Updated: November 21, 2024

🔗 References

https://success.trendmicro.com/solution/000289229 Patch,Vendor Advisory
https://success.trendmicro.com/solution/000289230 Patch,Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-1216/ Third Party Advisory,VDB Entry
https://success.trendmicro.com/solution/000289229 Patch,Vendor Advisory
https://success.trendmicro.com/solution/000289230 Patch,Vendor Advisory
https://www.zerodayinitiative.com/advisories/ZDI-21-1216/ Third Party Advisory,VDB Entry

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🔗 Related Vulnerabilities

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