SharedSecretClusterAuthenticator in Atlassian Bitbucket Data Center versions 5.14.0 and later before 7.6.14, 7.7.0 and later prior to 7.17.6, 7.18.0 and later prior to 7.18.4, 7.19.0 and later prior to 7.19.4, and 7.20.0 allow a remote, unauthenticated attacker to execute arbitrary code via Java deserialization.
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.