mercurial is vulnerable to authorization bypasses. The application does not check for access permissions if the wire protocol command if has no permissions declared, allowing a malicious user to gain unauthorized access to a repository.
access.redhat.com/errata/RHSA-2019:2276
lists.debian.org/debian-lts-announce/2018/03/msg00034.html
lists.debian.org/debian-lts-announce/2018/07/msg00005.html
lists.debian.org/debian-lts-announce/2020/07/msg00032.html
www.mercurial-scm.org/repo/hg/rev/2ecb0fc535b1
www.mercurial-scm.org/wiki/WhatsNew#Mercurial_4.5.1_.2F_4.5.2_.282018-03-06.29