CVE-2021-39325Network attack vector

Script execution via unvalidated preview input

Published Sep 20, 2021 · Updated Mar 31, 2025

Reflected XSS in OptinMonster 2.6.0 and earlier allows remote attackers to execute scripts in a visitor's browser through a crafted preview request. The load_previews function in OMAPI/Output.php insufficiently validates preview request input before incorporating it into web output. Exploitation requires a visitor to open an attacker-crafted request, allowing script execution in that visitor's browser context.

CVSS severity6.1
Medium
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Reflected XSS in OptinMonster 2.6.0 and earlier allows remote attackers to execute scripts in a visitor's browser through a crafted preview request. The load_previews function in OMAPI/Output.php insufficiently validates preview request input before incorporating it into web output. Exploitation requires a visitor to open an attacker-crafted request, allowing script execution in that visitor's browser context.

The record

CVE
CVE-2021-39325
Published
Sep 20, 2021
Updated
Mar 31, 2025
Vendor
OptinMonster
Product
OptinMonster
Classifications
CWE-79, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Mar 31, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=2.6.0 <=2.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OptinMonster · OptinMonsterversion=2.6.0 <=2.6.0

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1WordfenceCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.002User Execution: Malicious File

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo