CVE-2021-31521Network attack vector

Authenticated script execution via Captive Portal reflection

Published Jun 17, 2021 · Updated Aug 3, 2024

Reflected XSS in Trend Micro InterScan Web Security Virtual Appliance 6.5 SP2 allows remote authenticated users to run script in a victim's browser. Trend Micro identifies the Captive Portal as the affected locus but has not disclosed the endpoint, parameter, or faulty reflection operation. A low-privileged session and a victim rendering the crafted response are required, limiting impact to browser-context data access and actions.

CVSS severity6.3
Medium
EPSS probability1.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Trend Micro InterScan Web Security Virtual Appliance 6.5 SP2 allows remote authenticated users to run script in a victim's browser. Trend Micro identifies the Captive Portal as the affected locus but has not disclosed the endpoint, parameter, or faulty reflection operation. A low-privileged session and a victim rendering the crafted response are required, limiting impact to browser-context data access and actions.

The record

CVE
CVE-2021-31521
Published
Jun 17, 2021
Updated
Aug 3, 2024
Vendor
Trend Micro
Product
InterScan Web Security Virtual Appliance
Classifications
CWE-79, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=6.5 SP2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Trend Micro · InterScan Web Security Virtual Applianceversion=6.5 SP2

Published CVSS scores

3.5NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
6.3Trend MicroCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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