CVE-2020-24557: Trend Micro Multiple Products Improper Access Control Vulnerability

CVE-2020-24557 is an improper access control vulnerability in Trend Micro Apex One, OfficeScan, and Worry-Free Business Security on Microsoft Windows. An attacker who can manipulate a particular product folder may temporarily disable the security software, abuse a specific Windows function, and escalate privileges. For IT and security teams running these endpoint products, the issue matters because it can undermine the very controls meant to protect the host and open a path to higher privileges on the system.

Public detail is limited to the CISA description and the vendor products named above. Confirm exact affected builds, fixed versions, and deployment guidance directly against the Trend Micro advisory before acting.

How it works

The flaw is an improper access control weakness in the named Trend Micro products. In practical terms, the software does not sufficiently restrict what can be done to a particular product folder on the Windows host. An attacker who already has some level of access on the machine may manipulate that folder in a way that temporarily disables the security product. With protection weakened or off, the attacker can then abuse a specific Windows function to escalate privileges.

This is a local privilege-escalation style issue rather than a remote unauthenticated wormable flaw. Exploitation depends on the attacker already being able to interact with the affected product’s folder structure on the endpoint. Exact mechanics, prerequisites, and any required user interaction are not fully detailed in the public summary; treat the CISA description as the authoritative high-level picture and verify technical specifics in the vendor advisory.

Am I affected? How to find it in your systems

These products are typically deployed as endpoint security agents on Windows workstations and servers—Apex One and OfficeScan in enterprise environments, Worry-Free Business Security more often in smaller or mid-size deployments. Inventory every Windows host that runs a Trend Micro agent from this product family.

• Query your software inventory, EDR, or configuration-management database for installed Trend Micro Apex One, OfficeScan, or Worry-Free Business Security agents.
• On individual hosts, check Add/Remove Programs, the Trend Micro console, or agent version reporting to identify the product and build in use.
• Compare those versions and configurations against the list of affected and fixed releases in the official Trend Micro advisory; do not rely on version guesses.
• Review agent health and management-console alerts for unexpected disablement or protection-status changes that could indicate folder manipulation or temporary security bypass.
• Examine Windows security and application logs, and any Trend Micro diagnostic or audit logs, for anomalous activity around product directories or privilege-escalation indicators after suspected compromise.

If you cannot confirm the exact build, assume the host may be in scope until the vendor advisory rules it out.

How to remediate

Patch first. Apply the updates Trend Micro released for this vulnerability, following the vendor’s instructions exactly as stated in the advisory. CISA’s required action is to apply updates per vendor instructions; that remains the primary fix.

• Identify all managed and unmanaged endpoints running the affected products.
• Stage and deploy the vendor-supplied update through your normal change process, prioritizing internet-facing or high-value systems if you must phase the rollout.
• Verify successful update via the management console or local agent version checks, and confirm that protection features are fully re-enabled after the update.
• After patching, re-baseline agent health monitoring so that any future unexpected disablement stands out.

As general hardening for this class of issue, ensure endpoint agents run with least privilege where the product allows it, restrict who can write to security-product directories, and keep host-based application control or tamper-protection features enabled per vendor guidance.

If you can't patch immediately

If you cannot apply the vendor update at once, reduce risk with compensating controls until you can.

• Segment and prioritize: isolate high-risk or high-value Windows hosts that still run the vulnerable agent; limit lateral movement paths to those systems.
• Harden local access: restrict interactive and administrative logons on affected endpoints; enforce strong local credentials and just-in-time admin where possible so an attacker is less likely to reach the product folder in the first place.
• Tamper and integrity monitoring: enable or tighten any built-in tamper protection the product offers; monitor the product installation directories for unauthorized changes with file-integrity or EDR rules.
• Virtual patching / detection: if your EDR or host firewall can alert on or block processes that disable security agents or perform suspicious privilege-escalation patterns, enable those detections. Confirm any signatures or rules against current vendor and community guidance rather than inventing custom exploit logic.
• Heightened monitoring: watch for sudden agent disablement, unexpected service stops, or privilege-escalation events on hosts still awaiting the patch; investigate promptly.

These steps do not replace the vendor update; they only buy time.

If your data may have been exposed

Actively exploited privilege-escalation vulnerabilities on endpoints can lead to full host compromise and subsequent data theft or ransomware staging, even when ransomware use of this specific CVE is not documented. If you have evidence of exploitation or unexplained agent disablement on vulnerable systems, follow your incident-response process: isolate affected hosts, preserve logs, rotate credentials that may have been exposed, and assess what data the elevated attacker could have reached. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data to see whether your accounts already appear in public breach corpora.