Flagvent 2025: Hidden 3

FV25.H3 - Sneaky Elves

This hidden was discovered while solving the challenge: FV25.14 - the-prng

Solution

The Dockerfile contained a suspicious Docker image, ghcr.io/flagvent/challenges/alpine-stable:1.0. Exploring it on GitHub reveals the manifest for the image, which contains a label with the hidden flag:

{
  "digest": "sha256:cd7da0e2ba7d337c6bf25301d9bd6fcc3205e577145a3cae4a15a42a4cca4693",
  "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
  "size": 528,
  "config": {
    "digest": "sha256:c5abae227e2832d9f8ce0825b03cb478270528412bfe492042eefbc4855ddd9a",
    "mediaType": "application/vnd.docker.container.image.v1+json",
    "size": 1769
  },
  "layers": [
    {
      "digest": "sha256:014e56e613968f73cce0858124ca5fbc601d7888099969a4eea69f31dcd71a53",
      "mediaType": "application/vnd.oci.image.layer.v1.tar+gzip",
      "size": 3859315
    },
    {
      "digest": "sha256:c5abae227e2832d9f8ce0825b03cb478270528412bfe492042eefbc4855ddd9a",
      "mediaType": "text/plain; charset=utf-8",
      "size": 1769
    }
  ],
  "labels": {
    "org.flagvent.hidden-flag": "FV25{h1dden_1n_d0cker}"
  }
}

Flag:

FV25{h1dden_1n_d0cker}