Here's a Dockerfile that meets your requirements:

```Dockerfile
FROM docker.elastic.co/elasticsearch/elasticsearch:7.17.23

# Disable Elasticsearch security
RUN echo "xpack.security.enabled: false" >> /usr/share/elasticsearch/config/elasticsearch.yml

# Install the ingest-attachment plugin
RUN bin/elasticsearch-plugin install --batch ingest-attachment
```

This Dockerfile will:
1. Use the official Elasticsearch 7.17.23 image as the base
2. Append "xpack.security.enabled: false" to the elasticsearch.yml configuration file
3. Install the ingest-attachment plugin in non-interactive mode using the --batch flag

To build and use this image:
1. Save the Dockerfile
2. Run `docker build -t elasticsearch-ingest .`
3. Start a container with `docker run -p 9200:9200 -p 9300:9300 elasticsearch-ingest`

Note: The `--batch` flag is used to ensure the plugin installation runs in non-interactive mode, which is necessary for automated builds. The security configuration is appended to the existing elasticsearch.yml file that comes with the base image.