Bitbucket 8.18+ will ship with some more secure default settings. One of these is Hook Script support. This feature (intentionally) allows a SYS_ADMIN user to be able to upload scripts that will be executed by Git, as the operating system user.

Beginning with Bitbucket 8.17 this feature will be disabled by default, it will not be possible (by default) to upload new or updated scripts and existing scripts will cease to be called while the feature is disabled.

For instances that actually require hook script support the following should be set in $BITBUCKET_HOME/shared/bitbucket.properties:

feature.hook.scripts=true

When upgrading an existing instance that needs this feature enabled, you can add this setting prior to upgrade.