Date: Fri, 13 Jan 2017 07:13:46 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-bugs@FreeBSD.org Subject: [Bug 216014] /etc/shells security vagueness affecting ports Message-ID: <bug-216014-8@https.bugs.freebsd.org/bugzilla/>
next in thread | raw e-mail | index | archive | help
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D216014 Bug ID: 216014 Summary: /etc/shells security vagueness affecting ports Product: Base System Version: CURRENT Hardware: Any OS: Any Status: New Severity: Affects Some People Priority: --- Component: misc Assignee: freebsd-bugs@FreeBSD.org Reporter: freebsd@phil.spodhuis.org The shells(5) manpage describes /etc/shells as "a list of the shells on the system". The top of /usr/src/etc/shells documents the historical meaning: # List of acceptable shells for chpass(1). # Ftpd will not allow users to connect who are not using # one of these shells. My recollection is that 20 years ago, it was considered a security flaw for /etc/shells to list an untrusted shell, as the whole point was to define "i= f a user has one of these shells, then they're trusted for local system access". Indeed, /usr/bin/chpass is setuid-root and uses "ok_shell()" to enforce exa= ctly this behavior; so if arbitrary code can be gotten running as uid N, it can invoke chpass to change shell to any shell listed in /etc/shells, as long as the current shell is listed in that file too. Thus providing a privilege escalation attack. Yet the standard behavior of Ports is to add _all_ shells, including restri= cted shells, to /etc/shells. grep '^@shell' /usr/ports/shells/*/pkg-plist rbash, rzsh, scponly; also devel/git adds libexec/git-core/git-shell too. Users with any of those should _not_ be able to change their shell. The on= ly reason I can think of to add these shells to /etc/shells is some gateway software deciding to only allow access if the shell is listed and so reject= ing restricted shells ... which is a bug. So either the description in /usr/src/etc/shells is wrong and chpass is a security hole, or the man-page shells(5) is wrong and has led to many Ports being configured to introduce security holes when installed. --=20 You are receiving this mail because: You are the assignee for the bug.=
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?bug-216014-8>