Hi and thanks a lot for the report.
For security reports, please don't report them in the forum but stick to the process laid out in Free and Open Search: The Creators of Elasticsearch, ELK & Kibana | Elastic.
For this particular case it seems like a false positive.
The CVE is about the slf4j-ext module which the agent does not use. We only use slf4j-api which does not contain the vulnerable org.slf4j.ext.EventData class.
Nevertheless, I'll update the slf4j version and make sure we'll stay up to date with new versions: Update slf4j and add to dependabot allow list by felixbarny · Pull Request #1669 · elastic/apm-agent-java · GitHub