CVE-2026-105867Payload is a free and open source headless content management system. In @payloadcms/storage-s3 versions before 3.90.0 and canary versions before 4.0.0-canary.34, an authenticated user can overwrite an existing S3 object belonging to another upload collection when client uploads are enabled for multiple collections sharing a bucket and useCompositePrefixes is false or unset. This bypasses the target collection's access controls and prior file validation. This issue is fixed in versions 3.90.0 and 4.0.0-canary.34.