# CVE-2021-21265: October CMS vulnerable to Potential Host Header Poisoning on misconfigured servers

> Attackers can poison host headers on misconfigured October CMS servers to redirect users, requiring trusted host configuration or an upgrade.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Mar 2021
- **Updated:** 29 May 2025
- **Also known as:** GHSA-xhfx-hgmf-v6vp

## What is CVE-2021-21265?

CVE-2021-21265 is a medium-severity vulnerability in Octobercms October, published on 10 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

October is a free, open-source, self-hosted CMS platform based on the Laravel PHP Framework. In October before version 1.1.2, when running on poorly configured servers (i.e. the server routes any request, regardless of the HOST header to an October CMS instance) the potential exists for Host Header Poisoning attacks to succeed. This has been addressed in version 1.1.2 by adding a feature to allow a set of trusted hosts to be specified in the application. As a workaround one may set the configuration setting cms.linkPolicy to force.

Weakness: CWE-644 (Improper Neutralization of HTTP Headers for Scripting Syntax)

## Which versions are affected by CVE-2021-21265?

2 open source packages ship an affected version, including october/backend. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `october/backend` | Packagist | All versions | 1.1.2 |
| `october/backend` | Packagist | All versions | 1.1.2 |

Products: Octobercms October.

## How do I fix CVE-2021-21265?

Upgrade october/backend to 1.1.2 or later.

## Is CVE-2021-21265 being exploited?

There is no known exploitation of CVE-2021-21265 in the wild and no public exploit code.

## Other vulnerabilities in Octobercms October

- [CVE-2021-32648](https://insights.sbomify.com/CVE-2021-32648/): October CMS Improper Authentication (high 8.2, exploited in the wild)
- [CVE-2021-3311](https://insights.sbomify.com/CVE-2021-3311/): October CMS Session ID not invalidated after logout (critical 9.8)
- [CVE-2017-1000194](https://insights.sbomify.com/CVE-2017-1000194/): October CMS File Upload Vulnerability (critical 9.8)
- [CVE-2017-1000196](https://insights.sbomify.com/CVE-2017-1000196/): Code injection in n/a (critical 9.8)
- [CVE-2017-1000197](https://insights.sbomify.com/CVE-2017-1000197/): Path traversal in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21265 and fix it if it is affected.

What it is: CVE-2021-21265 is a medium-severity vulnerability in Octobercms October, published on 10 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-21265 in the wild and no public exploit code.

Affected packages and fixed versions:
- october/backend (Packagist): affected all versions; fixed in 1.1.2
- october/backend (Packagist): affected all versions; fixed in 1.1.2

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-2021-21265/ (Markdown: https://insights.sbomify.com/CVE-2021-21265/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21265
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21265
- OSV: https://osv.dev/vulnerability/CVE-2021-21265

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21265/
Summaries are generated and may contain mistakes; the official description above is the record.