• Exposed Google keys leaves billions of users open to mass spam and phishing notifications By CyberNews
• Bizarre Notifications Pop Up On Android Phones, Was A Hacker To Blame? By Forbes
• Google Firebase Cloud Messaging offers spam tier for some – no account required, just knowledge of bad security By TheRegister
• Fake Android notifications – first Google, then Microsoft affected By NakedSecurity Sophos
• Google Firebase exploit highlights risk of third-party development tools and potential phishing risks of new messaging platforms By Mimecast
• Google Firebase messaging vulnerability allowed attackers to send push notifications to app users By The Daily Swig

Blog Post References

• Intigriti Bug Bytes
• Android Police
• XDA Developers