In Mercurial before 4.1.3, “hg serve --stdio” allows remote authenticated users to launch the Python debugger, and consequently execute arbitrary code, by using --debugger as a repository name.
www.debian.org/security/2017/dsa-3963
www.securityfocus.com/bid/99123
access.redhat.com/errata/RHSA-2017:1576
bugs.debian.org/861243
github.com/advisories/GHSA-ghjx-3jg5-h6r2
lists.debian.org/debian-lts-announce/2018/07/msg00005.html
security.gentoo.org/glsa/201709-18
www.mercurial-scm.org/repo/hg/rev/77eaf9539499
www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.1.3_.282017-4-18.29