GHSA-jq29-c7v8-rg55

# Path Traversal in MediaUploadTrait::deleteFile() Allows Arbitrary File Deletion

## Summary

A path traversal vulnerability in `MediaUploadTrait::deleteFile()` allows an authenticated user with media management permissions to delete arbitrary files on the server. The method validates only the basename portion of the filename using `Utils::checkFilename()`, while the directory path (which may contain `../` sequences) is preserved and passed unvalidated to `unlink()`. This enables directory escape from the intended media storage path.

## Severity

**High (8.1)** - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H

## CWE

CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

## Details

In `system/src/Grav/Common/Media/Traits/MediaUploadTrait.php`, the `deleteFile()` method (lines 332-365) performs filename validation only on the basename, not the full path:

```php public function deleteFile(string $filename, ?array $settings = null): void { $settings = $this->getUploadSettings($settings); $filesystem = Filesystem::getInstance(false);

// Line 339-340: Only the BASENAME is validated $basename = $filesystem->basename($filename); // e.g. "evil.jpg" from "../../evil.jpg" if (!Utils::checkFilename($basename)) { // passes - no traversal in basename throw new RuntimeException(/* ... */); }

$path = $settings['destination'] ?? $this->getPath(); // ...

// Line 353: Full pathname (with traversal) is preserved $pathname = $filesystem->pathname($filename); // "../../"

// Line 356-357: Traversal path reconstructed [$base, $ext,,] = $this->getFileParts($basename); $name = "{$pathname}{$base}.{$ext}"; // "../../evil.jpg"

// Line 360: Passed to doRemove() $this->doRemove($name, $path); } ```

`doRemove()` (line 521-582) then calls:

```php // Line 538 unlink("{$folder}/{$filename}"); // e.g. unlink("/var/www/grav/user/pages/mypage/../../config/system.yaml") ```

`Utils::checkFilename()` (lines 1022-1044) properly checks for `/`, `\`, and `..`, but it is applied to `$filesystem->basename($filename)` (the last path component only), so traversal sequences in the directory portion are never validated.

### Data flow from user input

The vulnerability is reachable through the Flex media handling pipeline:

1. `FlexMediaTrait::setUpdatedMedia()` (line 386) iterates form flash data where `$filename` is the array key - user-controlled 2. For file deletions (`$file` is null, line 396), NO upload validation is performed (the `checkUploadedFile()` call at line 401 only executes when `$file` is truthy) 3. The raw filename is stored in `$this->_uploads` at line 414 4. `saveUpdatedMedia()` (line 499) calls `$media->deleteFile($filename, $settings)` with the unsanitized filename

### Sibling: renameFile()

The same pattern exists in `renameFile()` (lines 374-405) which has even weaker validation - it performs NO `checkFilename()` call at all. While `renameFile()` currently has no callers in the core codebase, it is part of the public `MediaUploadInterface` and should be fixed as defense-in-depth.

## Proof of Concept

**Environment**: Grav CMS 2.0.16 with admin plugin

The attack requires an authenticated admin user with page/media editing permissions (not super-admin).

1. Create a target file: ```bash echo "DELETE_ME" > /var/www/grav/user/data/target.txt ```

2. Submit a Flex object form (e.g. page edit) with a crafted media deletion where the filename key contains path traversal:

``` POST /admin/pages/mypage/task:save Content-Type: multipart/form-data

# The form flash data includes a media deletion entry with key: # "../../data/target.txt" -> null (deletion marker) ```

3. When `saveUpdatedMedia()` processes the deletion queue: - `$filename` = `../../data/target.txt` - `deleteFile("../../data/target.txt")` is called - `$basename` = `target.txt` (passes `checkFilename()`) - `$pathname` = `../../data/` - `$name` = `../../data/target.txt` - `doRemove()` calls `unlink("/var/www/grav/user/pages/mypage/../../data/target.txt")` - Which resolves to `unlink("/var/www/grav/user/data/target.txt")`

4. The file is deleted outside the intended media directory.

### Impact

An authenticated user with media management permissions can: - Delete configuration files (`user/config/system.yaml`, `user/config/security.yaml`) - Delete other pages' content files - Delete authentication-related files (user account YAML files) - Cause denial of service by removing critical application files - Potentially escalate privileges by removing security configuration

## Suggested Fix

Apply `Utils::checkFilename()` to the full `$filename` parameter before decomposing it, or reject any filename containing directory separators or `..` sequences:

```php public function deleteFile(string $filename, ?array $settings = null): void { $settings = $this->getUploadSettings($settings); $filesystem = Filesystem::getInstance(false);

// Validate the FULL filename, not just the basename if (!Utils::checkFilename($filename)) { throw new RuntimeException(/* ... */); }

// ... rest unchanged } ```

The same fix should be applied to `renameFile()` for both `$from` and `$to` parameters.

## References

- Vulnerable file: `system/src/Grav/Common/Media/Traits/MediaUploadTrait.php` lines 332-365, 521-582 - Caller: `system/src/Grav/Framework/Flex/Traits/FlexMediaTrait.php` lines 386-414, 490-499 - Sibling: `system/src/Grav/Common/Media/Traits/MediaUploadTrait.php` lines 374-405 (renameFile) - Related GHSA: GHSA-g6j3-8jv9-ch5f (path traversal in PagesController::batchCopy - different file, same bug class)

## Disclosure

This vulnerability was discovered using AI-assisted security research tools.