Craft CMS versions >= 5.0.0-RC1 and < 5.10.11 contain a missing authorization vulnerability in AssetsController::actionReplaceFile. When a request supplies sourceAssetId and targetFilename but omits assetId, the target asset is resolved by folder and filename after the permission checks execute, so the replacePeerFiles permission is never enforced. An authenticated low-privilege author with only the replaceFiles permission on a shared folder can overwrite the content of a peer's asset file (located in the same folder) with attacker-controlled bytes. Fixed in 5.10.11.

Craft CMS versions >= 5.0.0-RC1 and < 5.10.11 contain a missing authorization vulnerability in AssetsController::actionReplaceFile. The flaw allows an authenticated low-privilege author to bypass the replacePeerFiles permission check by omitting the assetId parameter from a request. When sourceAssetId and targetFilename are supplied without assetId, the target asset is resolved by folder and filename after permission checks have already executed, meaning the replacePeerFiles permission is never enforced. This enables an attacker with only the replaceFiles permission on a shared folder to overwrite a peer's asset file with attacker-controlled bytes. The vulnerability is an authorization logic flaw stemming from the order of operations in the permission enforcement flow. It requires authentication but only low-privilege access. The issue has been patched in Craft CMS version 5.10.11.