The open_envvar function in xdg-open in xdg-utils before 1.1.3 does not validate strings before launching the program specified by the BROWSER environment variable, which might allow remote attackers to conduct argument-injection attacks via a crafted URL, as demonstrated by %s in this environment variable.
https://www.debian.org/security/2018/dsa-4211
https://usn.ubuntu.com/3650-1/
https://lists.debian.org/debian-lts-announce/2018/05/msg00014.html
https://cgit.freedesktop.org/xdg/xdg-utils/tree/ChangeLog
https://cgit.freedesktop.org/xdg/xdg-utils/commit/?id=ce802d71c3466d1dbb24f2fe9b6db82a1f899bcb
https://cgit.freedesktop.org/xdg/xdg-utils/commit/?id=5647afb35e4bcba2060148e1a2a47bc43cc240f2