CVE Intelligence
CISA KEV High File handling

CVE-2021-36741 — Trend Micro Multiple Products Improper Input Validation Vulnerability

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.

Published Jul 29, 2021 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, NIST National Vulnerability Database, GitHub Security Advisories, CVE Program (cve.org) e CISA ADP · CNA: trendmicro

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Nov 3, 2021
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • EPSS 5% (30-day exploitation probability)+14
  • Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Nov 3, 2021
EPSS FIRST
4.95%
ahead of 92% of scored CVEs · Oct 14, 2026
Affects
Trend Micro, Inc.
Apex One and 3 more
CVSS base
8.8
High · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: Nov 17, 2021 — passed 1793 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Trend Micro, Inc. Apex One, Trend Micro, Inc. Officescan, Trend Micro, Inc. Officescan Business Security…).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. EPSS ahead of 92% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes matching the vulnerability class (file handling), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Trend Micro, Inc. Apex One version 2019 Vulnerable NIST National Vulnerability Database
Trend Micro, Inc. Apex One version 2019, SaaS Vulnerable CVE Program (cve.org) e CISA ADP
Trend Micro, Inc. Officescan version xg-sp1 Vulnerable NIST National Vulnerability Database
Trend Micro, Inc. Officescan version XG SP1 Vulnerable CVE Program (cve.org) e CISA ADP
Trend Micro, Inc. Officescan Business Security version 10.0-sp1 Vulnerable NIST National Vulnerability Database
Trend Micro, Inc. Worry-free Business Security version 10.0-sp1 Vulnerable NIST National Vulnerability Database
Trend Micro, Inc. Worry-free Business Security version 10.0 SP1 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
8.8 CVSS 3.1 High 2.8 5.9 nvd@nist.gov via NIST National Vulnerability Database
8.8 CVSS 3.1 High 2.8 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
8.8 CVSS 3.1 High — — GitHub, Inc. via GitHub Security Advisories
8.8 CVSS 3.1 High — — CISA-ADP via CVE Program (cve.org) e CISA ADP
6.5 CVSS 2.0 Medium 8.0 6.4 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-434 · Unrestricted Upload of File with Dangerous Type

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Nov 3, 2021
Federal deadline
Nov 17, 2021
passed 1793 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 4.95%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Monitor file creation in web directories and paths with traversal sequences (../).
  • Hunt retroactively in logs from before Nov 3, 2021 (KEV listing): exploitation may have started earlier.
web/proxy/WAF logsnetwork IDS/IPSfile integrity (FIM)endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · trend micro/trend micro apex one, trend micro/trend micro officescan, trend micro/trend micro worry-free business securi
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Affected products added · trendmicro/officescan, trendmicro/officescan business security, trendmicro/apex one, trendmicro/worry-free business secu
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 8.8
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2021
  • Added to CISA KEV catalog
    Nov 2, 2021 · CISA
  • CVE published
    Jul 29, 2021 · trendmicro

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

7 on the record

Elsewhere on this site

Trend Micro, Inc.
every CVE for this vendor
2021-11
what else CISA listed that month
File handling
same class
CWE-434
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-45208 TOCTOU Race Condition in Trend Micro, Inc. Apex One May 21, 2026
  • CVE-2026-45207 An origin validation vulnerability in the Apex One/SEP agent could allow a local… May 21, 2026
  • CVE-2026-45206 An origin validation vulnerability in the Apex One/SEP agent could allow a local… May 21, 2026
  • CVE-2026-34928 An origin validation vulnerability in the Apex One/SEP agent could allow a local… May 21, 2026
  • CVE-2026-34927 An origin validation vulnerability in the Apex One/SEP agent could allow a local… May 21, 2026
  • CVE-2026-34926 Trend Micro Apex One (On-Premise) Directory Traversal Vulnerability KEV May 21, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-36741 is "Trend Micro Multiple Products Improper Input Validation Vulnerability", rated High. It affects Apex One (Trend Micro, Inc.); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 8.8 describes technical severity. EPSS 4.95% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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