CVE-2021-39341Known exploitationNetwork attack vector

API-key disclosure via forged REST request headers

Published Nov 1, 2021 · Updated Mar 31, 2025

Incorrect authorization in OptinMonster 2.6.4 and earlier allows remote attackers to disclose API keys through WordPress REST endpoints. The logged_in_or_has_api_key permission callback in OMAPI/RestApi.php returns true for an OPTIONS request whose Referer contains a trusted test URL, while X-HTTP-Method-Override supplies the protected GET or POST method. No WordPress account is required; a disclosed key grants campaign access for placing malicious JavaScript on connected sites.

CVSS severity8.2
High
EPSS probability21.93%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in OptinMonster 2.6.4 and earlier allows remote attackers to disclose API keys through WordPress REST endpoints. The logged_in_or_has_api_key permission callback in OMAPI/RestApi.php returns true for an OPTIONS request whose Referer contains a trusted test URL, while X-HTTP-Method-Override supplies the protected GET or POST method. No WordPress account is required; a disclosed key grants campaign access for placing malicious JavaScript on connected sites.

The record

CVE
CVE-2021-39341
Published
Nov 1, 2021
Updated
Mar 31, 2025
Vendor
OptinMonster
Product
OptinMonster
Classifications
CWE-863, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 1, 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

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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=2.6.4 <=2.6.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OptinMonster · OptinMonsterversion=2.6.4 <=2.6.4

Published CVSS scores

8.2WordfenceCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 exploitationReported
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1190Exploit Public-Facing Application

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.

Reported exploitation

Technologies

Your stack

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Your stack

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