The FIRST Guidelines and Practices for Multi-Party Vulnerability Coordination and Disclosure provides guidelines on how to handle end-to-end the process of managing vulnerability disclosure from prior the disclosure (e.g. providing clear communication channels) to after disclosure.
Reference
FIRST Guidelines and Practices for Multi-Party Vulnerability Coordination and Disclosure v1.1: https://www.first.org/global/sigs/vulnerability-coordination/multiparty/guidelines-v1.1
Related: #22