CVE-2026-27937

A vulnerability was detected in October CMS up to 4.3.4. This affects the function validateExternalImageHost of the file System/Classes/ResizeImages.php of the component SSRF Protection. The manipulation results in server-side request forgery. The attack may be launched remotely, and the exploit is now public.

October CMS through 1.0.428 does not prevent the use of .htaccess in themes, allowing remote authenticated users to execute arbitrary PHP code by downloading a theme ZIP archive from /backend/cms/themes, and then uploading and importing a modified archive with two new files: a .php file and a .htaccess file.

October CMS version 412 is vulnerable to PHP object injection in asset move functionality, allowing for the deletion of files limited by file permissions on the server.

October CMS version 412 is vulnerable to PHP code execution in the file upload functionality, potentially leading to site compromise and possibly affecting other applications on the server.

October CMS version 412 is vulnerable to file path modification in asset move functionality, potentially allowing the creation of malicious files on the server.

October CMS version 412 is vulnerable to PHP code execution in the asset manager functionality, potentially leading to site compromise and possibly affecting other applications on the server.

October CMS build 412 is vulnerable to Apache configuration modification via file upload functionality, potentially leading to site compromise and affecting other applications on the server.

October CMS versions prior to 3.7.17 and 4.2.21 contain a PHP object injection vulnerability in the system module. The backend `SessionMaker` trait stored widget session state as `base64(serialize(...))` and consumed it with `unserialize()` without an `allowed_classes` restriction, allowing attacker-controlled bytes to trigger object injection and reachable PHP gadget chains. This issue only affects installations with `cms.safe_mode` enabled, which is an opt-in feature for demo or multi-tenant scenarios.

A vulnerability in the October CMS system module's Twig sandbox security policy allowed a chained bypass when cms.safe_mode is enabled. By combining unrestricted access to the Laravel session store with unblocked raw SQL methods reachable through Eloquent's __call forwarding, a backend user with CMS markup editing access could read arbitrary database values and write to the backend authentication session key, forging a session as another existing user. The issue is patched in versions 3.7.17 and 4.2.21.