Please report it privately, through GitHub's private vulnerability reporting rather than as a public issue. That way it can be fixed and released before it is described in public.

Say what you found, how to reach it, and which version — Settings → About has it. A first reply should come within a few days.

Dermaga runs Apple's container CLI as you, on your machine, and its own agent listens on a socket in your home directory. So the things worth looking at are the ones where that boundary could be crossed:

• The update mechanism. Dermaga replaces itself with a downloaded build after checking its signature, its team identifier and its notarization. A way past those checks would mean arbitrary code arriving as an update.
• The agent socket. ~/.dermaga/agent.sock is created for the current user only. Anything reachable through it that should not be, or a way for another user to reach it, is a finding.
• Command construction. Everything eventually becomes an argument to a CLI. A container name, an image reference or a volume owner that escapes into a shell rather than staying an argument is a finding.
• Credentials. Registry passwords go to Apple's CLI on stdin and are never written down here. Somewhere they end up anyway is a finding.

Apple's container runtime, Homebrew and Trivy are separate projects with their own reporting. A vulnerability in the images you scan is what Dermaga is for; report those to whoever publishes the image.

• It opens no ports. The app and its agent speak over a Unix socket in your home directory, created with permissions for you alone.
• Releases are signed with an Apple Developer ID and notarized by Apple. The app and the disk image are both stapled, so a Mac with no network can still verify them.
• An update is only installed in place after its signature verifies, its team matches the running copy, and Gatekeeper accepts it. Anything short of that falls back to opening the disk image and letting you decide.
• Nothing about your containers, images or scan results is sent anywhere. The only things fetched are the app's own updates, and the CLI and scanner it installs through Homebrew.

The latest release. Fixes go into the next one rather than into patches of older versions.