Dulwich before 0.18.5, when an SSH subprocess is used, allows remote attackers to execute arbitrary commands via an ssh URL with an initial dash character in the hostname, a related issue to CVE-2017-9800, CVE-2017-12836, CVE-2017-12976, CVE-2017-1000116, and CVE-2017-1000117.
https://www.dulwich.io/code/dulwich/commit/7116a0cbbda571f7dac863f4b1c00b6e16d6d8d6/