The issue allows remote command execution through the "go get" command. By using custom domains, an attacker can trick "go get" into reusing a Git checkout from a Subversion repository, potentially executing malicious commands in .git/hooks/ on the system running "go get". This can be achieved by arranging custom domains so that example.com/pkg1 points to a Subversion repository and example.com/pkg1/pkg2 points to a Git repository, and including a Git checkout in the Subversion repository's pkg2 directory.