In Octopus Deploy 3.x before 3.15.4, an authenticated user with PackagePush permission to upload packages could upload a maliciously crafted NuGet package, potentially overwriting other packages or modifying system files. This is a directory traversal in the PackageId value.
In affected versions of Octopus Server with certain access levels it was possible to embed a Cross-Site Scripting payload on the audit page.