What is CVE-2021-4226?

CVE-2021-4226 is a critical-severity vulnerability in Rsjoomla Rsfirewall\!, classified under Insufficient Verification of Data Authenticity. CVSS score: 9.8/10. Published 2022-12-15.

How severe is CVE-2021-4226?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-4226 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Rsjoomla Rsfirewall\!

CVE-2021-4226

RSFirewall tries to identify the original IP address by looking at different HTTP headers. A bypass is possible due to the way it is implemented.

Published 2022-12-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.005 (41.6th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 42nd percentile — 41.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: +0.000

Affected products

Rsjoomla Rsfirewall\!
Rsfirewall! — versions 0

Weakness classification (CWE)

CWE-345 — Insufficient Verification of Data Authenticity

Public proof-of-concept exploits

20142995/nuclei-templates

References

wpscan.com/vulnerability/c0ed80c8-ebbf-4ed9-b02f-31660097c352 (Exploit, technical-description, Third Party Advisory, exploit, vdb-entry)

Frequently asked questions

What is CVE-2021-4226?: CVE-2021-4226 is a critical-severity vulnerability in Rsjoomla Rsfirewall\!, classified under Insufficient Verification of Data Authenticity. CVSS score: 9.8/10. Published 2022-12-15.
How severe is CVE-2021-4226?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-4226 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.