Craft CMS: Unauthorized Deletion of Source Assets During File Replacement

We have identified an authorization issue in Craft CMS AssetsController::actionReplaceFile that can delete a source asset without source delete permission by supplying both assetId and sourceAssetId.

Description

Craft CMS’s craft\\controllers\\AssetsController::actionReplaceFile() supports replacing a target asset file using another existing asset as the source. The action loads:

• $assetToReplace from assetId
• $sourceAsset from sourceAssetId

It then enforces replace permissions using ($assetToReplace ?: $sourceAsset). When both IDs are provided, this expression resolves to the target asset so no permission check is performed against the source asset volume.

 1$this->requireVolumePermissionByAsset('replaceFiles', $assetToReplace ?: $sourceAsset);
 2$this->requirePeerVolumePermissionByAsset('replacePeerFiles', $assetToReplace ?: $sourceAsset);

src/controllers/AssetsController.php:L433-L434

In the branch where both assets are present, Craft copies the source file into the target and then deletes the source asset. There is no check for deleteAssets:<sourceVolumeUid> or deletePeerAssets:<sourceVolumeUid> for the source asset before deletion.

 1$assets->replaceAssetFile($assetToReplace, $tempPath, $assetToReplace->getFilename(), $sourceAsset->getMimeType());
 2Craft::$app->getElements()->deleteElement($sourceAsset);

src/controllers/AssetsController.php:L462-L463

Impact

An authenticated user who can replace files in one volume can delete assets in another volume where they do not have delete permission, as long as they can obtain a sourceAssetId. This can lead to unauthorized asset deletion, broken content references, and data loss.