Summary
October CMS vulnerable to Potential Host Header Poisoning on misconfigured servers
Workarounds
Apply https://github.com/octobercms/library/commit/f86fcbcd066d6f8b939e8fe897409d152b11c3c6 & https://github.com/octobercms/october/commit/f638d3f78cfe91d7f6658820f9d5e424306a3db0 to your installation manually if unable to upgrade to v1.1.2.
Check that the configuration setting
cms.linkPolicyis set toforce.
Alternative Workaround
Check to make sure that your web server does not accept any hostname when serving your web application.
- Add an entry called
testing.tldto your computer's host file and direct it to your server's IP address - Open the address
testing.tldin your web browser - Make sure an October CMS website is not available at this address
If an October CMS website is returned, configure your webserver to only allow known hostnames. If you require assistance with this, please contact your server administrator.
References
Reported by Abdullah Hussam
For More Information
If you have any questions or comments about this advisory:
- Email us at [email protected]
Threat Assessment
Impact
When running on servers that are configured to accept a wildcard as a hostname (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. See the following resources for more information on Host Header Poisoning:
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
A feature has been added in v1.1.2 to allow a set of trusted hosts to be specified in the application.
Frequently Asked Questions
- What is CVE-2021-21265? CVE-2021-21265 is a low-severity security vulnerability in october/backend (composer), affecting versions < 1.1.2. It is fixed in 1.1.2.
- Which versions of october/backend are affected by CVE-2021-21265? october/backend (composer) versions < 1.1.2 is affected.
- Is there a fix for CVE-2021-21265? Yes. CVE-2021-21265 is fixed in 1.1.2. Upgrade to this version or later.
- Is CVE-2021-21265 exploitable, and should I be worried? Whether CVE-2021-21265 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-21265 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-21265? Upgrade
october/backendto 1.1.2 or later.