Atlassian Connect Spring Boot is a Java Spring Boot package for building Atlassian Connect apps. Authentication between Atlassian products and the Atlassian Connect Spring Boot app occurs with a server-to-server JWT or a context JWT. Atlassian Connect Spring Boot versions between 1.1.0 - 2.1.2 erroneously accept context JWTs in lifecycle endpoints (such as installation) where only server-to-server JWTs should be accepted, permitting an attacker to send authenticated re-installation events to an app. This is fixed in version 2.1.3.
1.1.0 - 2.1.2
2.1.3 and later
This is an independent assessment and you should evaluate its applicability to your own IT environment.
CVSS v3 score: 9.1 => Critical severity