GHSA-vj3m-2g9h-vm4p: Grav has multiple RCE vectors: unsafe unserialize (x3), command injection in git clone, SSTI blocklist bypass

Multiple RCE vectors were found in Grav CMS. Three are critical, two are high.

1. Unsafe unserialize() in JobQueue — direct RCE gadget (Critical)

system/src/Grav/Common/Scheduler/JobQueue.php:465 calls unserialize(base64_decode(...)) without restricting allowed_classes. The Job class has call_user_func_array($this->command, $this->args) in its execution path, which is a direct gadget chain — inject a serialized Job with command = 'system' and args = ['whoami'].

The same codebase actually has a Serializable trait that correctly restricts classes, so this inconsistency stands out.

2. Unsafe unserialize() in FileCache — arbitrary class instantiation (Critical)

system/src/Grav/Framework/Cache/Adapter/FileCache.php:75 does unserialize($value, ['allowed_classes' => true]). That true allows instantiation of any class. If an attacker can write to the cache directory (via any file write primitive), they get object injection → RCE.

3. Unsafe unserialize() in Session (High)

system/src/Grav/Common/Session.php:116 — same allowed_classes => true pattern on session data. Lower severity since session storage is typically more restricted.

4. Command injection in git clone (Critical)

system/src/Grav/Console/Cli/InstallCommand.php:150 — only $this->destination uses escapeshellarg(). The $data['branch'], $data['url'], and $data['path'] variables go directly into the shell command without escaping. Admin-accessible via plugin/theme installation.

5. SSTI blocklist bypass (High)

system/src/Grav/Common/Security.php:267-286 — cleanDangerousTwig() blocks twig_array_map and twig_array_filter but not twig_array_reduce. Also missing file_get_contents and fwrite from the dangerous function blocklist. An attacker who can inject Twig templates can bypass the security filter.

All five are independently exploitable. The unserialize issues are the most concerning since they don’t require admin access if there’s any file write primitive.

— ProScan AppSec | proscan.one