CVE-2021-39341: OptinMonster <= 2.6.4 Unprotected REST-API Endpoints
Vulnerability summary
CVE-2021-39341 is a high (CVSS 8.2) vulnerability in optinmonster. EPSS estimates a 21.93% chance of exploitation in the next 30 days, higher than 97.6% of scored vulnerabilities. 1 public exploit is recorded. Fixed in 2.6.5.
Timeline
- 01-11-2021PublishedVulnerability first disclosed.
- 31-03-2025Last modifiedVulnerability information updated.
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.
CVSS metrics
4 scores · 3 sources · 2 versions- NVDNIST8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
- wordfenceSource8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
EPSS trend
Probability
21.93%
Chance of exploitation in the next 30 days
Percentile
98%
Versus all other CVEs
30-day change
No change 0.00 pp
From 21.93% on 22-09-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
1 foundExploit Reference (wordfence.com)
Maturity: unknown
Weaknesses
CWE · root cause- CWE-319Cleartext Transmission of Sensitive InformationThe product transmits sensitive or security-critical data in cleartext in a communication channel that can be sniffed by unauthorized actors.
- CWE-863Incorrect AuthorizationThe product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
- CWE-285Improper AuthorizationThe product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
Affected systems
Optinmonster1 product
- optinmonster2.6.4 | ≤ 2.6.4
Wordpress1 product
- optinmonster≤ 2.6.4 (fixed in 2.6.5)
2 vendors · 2 products
References
4 links- www.wordfence.com/blog/2021/10/1000000-sites-affected-by-optinmonster-vulnerabilities/X Refsource MISCExploitThird Party Advisory
- plugins.trac.wordpress.org/browser/optinmonster/trunk/OMAPI/RestApi.php?rev=2606519X Refsource MISCThird Party Advisory