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Fencer Intel
high 8.2

CVE-2021-39341 in the critical feed json

OptinMonster <= 2.6.4 Unprotected REST-API Endpoints

published 5y ago modified 4mo ago also EUVD-2021-25702

cvss
8.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
21.9%
EPSS 21.9% chance of exploitation in 30 days, percentile 97%
public exploits
0
none known, plus a Nuclei check

Summary

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.

Is CVE-2021-39341 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last yr.

Exploit prediction

21.93% chance of exploitation in the next 30 days, higher than 97% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • Nuclei template OptinMonster Plugin < 2.6.5 - Unprotected REST-API nuclei detection template
  • wordfence.com https://www.wordfence.com/blog/2021/10/1000000-sites-affected-by-optinmonster-vulnerabilities/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
NVD 2.0 6.4 AV:N/AC:L/Au:N/C:P/I:P/A:N

Affected products

  • OptinMonster OptinMonster

Classification

Weakness
  • CWE-285 Improper Authorization
  • CWE-319 Cleartext Transmission of Sensitive Information
  • CWE-863 Incorrect Authorization
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.