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Date: Wed, 31 Jan 2024 23:58:40 +0100
From: Jakub Wilk <jwilk@...lk.net>
To: <oss-security@...ts.openwall.com>
CC: halfdog <me@...fdog.net>
Subject: Re: TTY handling when executing code in different
lower-privileged context (su, virt containers)
I'm a few years late, but hey.
* halfdog <me@...fdog.net>, 2012-11-05 19:22:
>The basic idea is, that a program started from interactive shell can
>access the TTY and also inject input data using TIOCSTI ioctl.
[…]
>In both cases, paranoid administrators might decide to use /dev/null as
>stdin/stdout/stderr
Redirecting unneeded fds is a good idea, but alone it's not sufficient
to defeat the attack. The unprivileged process could open /dev/tty and
then issue TIOCSTI on that fd.
>[1] http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation/
This insufficient work-around is also mentioned on the website:
"When no interactive shell is needed in lower-privileged context, su et
al. can be run with stdin, stdout, stderr redirection, not passing a
tty-fd to the other context"
--
Jakub Wilk
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