CVE-2021-39341
HighExploitedOptinMonster <= 2.6.4 - Unprotected REST-API Endpoints
Published Nov 2, 2021 · Updated Mar 31, 2025 · Also known as 77eb40c2-735a-49f2-9d07-5cf7535bd722
Key Facts
Patch immediately- CVE-2021-39341 is a high-severity vulnerability (CVSS 8.2 v3.1) affecting OptinMonster.
- It is exploited in the wild, listed in Industry KEV feed since Oct 27, 2021. No public exploit code is known.
- EPSS estimates a 22% probability of exploitation in the next 30 days.
- Fixed versions are available, including OptinMonster 2.6.5, OptinMonster <=2.6.4, OptinMonster 2.6.4.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
8.2
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
EPSS (30-day exploit likelihood)
22%
Higher than 97.6% of all scored CVEs
Exploited in the wild
Yes
1 catalog listing
Public exploit code
None known
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Description
The OptinMonster WordPress plugin is vulnerable to sensitive information disclosure and unauthorized setting updates due to insufficient authorization validation via the logged_in_or_has_api_key function in the ~/OMAPI/RestApi.php file that can used to exploit inject malicious web scripts on sites with the plugin installed. This affects versions up to, and including, 2.6.4.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| Industry KEV feed | Oct 27, 2021 | n/a | Not reported |
Required action: Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.
Affected Products
3 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| OptinMonsterOptinmonster | >= 2.6.4 | 2.6.4 |
Patched Releases
OptinMonster
2.6.5, <=2.6.4
Timeline
Added to Industry KEV feed
Oct 27, 2021
Publicly disclosed
Nov 2, 2021
Last updated
Mar 31, 2025
Weakness Type
- CWE-285 Improper Authorization
- CWE-319 Cleartext Transmission of Sensitive Information
- CWE-863 Incorrect Authorization
References
- advisoryhttps://plugins.trac.wordpress.org/browser/optinmonster/trunk/OMAPI/RestApi.php?rev=2606519#L1460
- advisoryhttps://portswigger.net/daily-swig/wordpress-plugin-vulnerability-opened-up-one-million-sites-to-remote-takeover?&web_view=true
- advisoryhttps://portswigger.net/daily-swig/wordpress-plugin-vulnerability-opened-up-one-million-sites-to-remote-takeover?&web_view=trueWordPress
- advisoryhttps://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-10001
- advisoryhttps://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2018-25019
FAQ
Common Questions.
The OptinMonster WordPress plugin is vulnerable to sensitive information disclosure and unauthorized setting updates due to insufficient authorization validation via the logged_in_or_has_api_key function in the ~/OMAPI/RestApi.php file that can used to exploit inject malicious web scripts on sites with the plugin inst…
Affected: OptinMonster versions >= 2.6.4. The full list is in the CVE brief.
It is exploited in the wild, listed in Industry KEV feed since Oct 27, 2021.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
Fixed versions are available, including OptinMonster 2.6.5, OptinMonster <=2.6.4, OptinMonster 2.6.4.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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