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Fencer Vulns
high 8.2

CVE-2021-39341 in the critical feed json

OptinMonster <= 2.6.4 Unprotected REST-API Endpoints

published 2021-11-01 5 y ago modified 2026-06-17 4 mo 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.

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
19 mo ago

Exploit prediction

21.93% chance of exploitation in the next 30 days, higher than 97% of all scored CVEs (FIRST EPSS, 2026-11-08).

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 Vulns 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.