CVE-2021-21264 — october/cms
MEDIUMCVE-2021-21264 is a medium-severity (CVSS 5.2) CWE-862 vulnerability in october/cms. A fix is available for october/cms — see the affected versions and patch details below.
Bypass of fix for CVE-2020-26231, Twig sandbox escape
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-21264 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
october/cms🐘october/cmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A bypass of CVE-2020-26231 (fixed in 1.0.470/471 and 1.1.1) was discovered that has the same impact as CVE-2020-26231 & CVE-2020-15247:
An authenticated backend user with the cms.manage_pages, cms.manage_layouts, or cms.manage_partials permissions who would normally not be permitted to provide PHP code to be executed by the CMS due to cms.enableSafeMode being enabled is able to write specific Twig code to escape the Twig sandbox and execute arbitrary PHP.
This is not a problem for anyone that trusts their users with those permissions to normally write & manage PHP within the CMS by not having cms.enableSafeMode enabled, but would be a problem for anyone relying on cms.enableSafeMode to ensure that users with those permissions in production do not have access to write & execute arbitrary PHP.
Patches
Issue has been patched in Build 472 (v1.0.472) and v1.1.2.
Workarounds
Apply https://github.com/octobercms/october/commit/f63519ff1e8d375df30deba63156a2fc97aa9ee7 to your installation manually if unable to upgrade to Build 472 or v1.1.2.
References
Reported by ka1n4t
For more information
If you have any questions or comments about this advisory:
- Email us at [email protected]
Threat assessment:
<img width="1108" alt="Screen Shot 2020-10-10 at 1 21 13 PM" src="https://user-images.githubusercontent.com/7253840/95663316-7de28b80-0afb-11eb-999d-a6526cf78709.png">Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | october/cms | ≥ 1.0.471&&< 1.0.472 | 1.0.472composer require october/cms:^1.0.472 |
| 🐘Packagist | october/cms | ≥ 1.1.1&&< 1.1.2 | 1.1.2composer require october/cms:^1.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for october/cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update october/cms to 1.0.472 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21264 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-21264 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-21264. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21264 in your dependencies?
O3 Security finds CVE-2021-21264 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.