# CVE-2021-4226: RSFirewall < 1.1.25 - IP Block Bypass

> Attackers can bypass IP blocking restrictions in RSFirewall by manipulating HTTP headers, allowing unauthorized access to protected resources.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Dec 2022
- **Updated:** 21 Apr 2025
- **Also known as:** GHSA-j8wj-77mv-262g

## What is CVE-2021-4226?

CVE-2021-4226 is a critical vulnerability in Unknown RSFirewall!, published on 15 Dec 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-345 (Insufficient Verification of Data Authenticity)

## Which versions are affected by CVE-2021-4226?

It affects 1 product.


Products: Rsjoomla Rsfirewall\!.

## How do I fix CVE-2021-4226?

No fix has been published for CVE-2021-4226 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-4226 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-4226 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4226 and fix it if it is affected.

What it is: CVE-2021-4226 is a critical vulnerability in Unknown RSFirewall!, published on 15 Dec 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-4226 exists.

Affected product: Unknown RSFirewall!. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-4226/ (Markdown: https://insights.sbomify.com/CVE-2021-4226/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4226
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4226
- OSV: https://osv.dev/vulnerability/CVE-2021-4226

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4226/
Summaries are generated and may contain mistakes; the official description above is the record.