A security flaw was found in the way "/dev/ptmx", a character device used to create a pseudo-terminal master (PTM) and slave (PTS) pair, of the Linux kernel, used to transmit data through the PTM when a keystroke was pressed. An unprivileged, local user could use this flaw to determine inter-keystroke timing (measure latency between keystrokes), possibly allowing them to determine effective length of an password being typed in. References: [1] http://vladz.devzero.fr/013_ptmx-timing.php [2] http://users.ece.cmu.edu/~dawnsong/papers/ssh-timing.pdf [3] http://www.openwall.com/lists/oss-security/2013/01/07/5 [4] https://bugzilla.novell.com/show_bug.cgi?id=797175 Reproducers: [5] http://vladz.devzero.fr/svn/codes/PoC/ptmx-keystroke-latency.c (to display latency between keystrokes) [6] http://vladz.devzero.fr/svn/codes/PoC/ptmx-su-pwdlen.sh (to determine password length) This issue was found by researcher with nickname vladz.
Created attachment 674721 [details] Local copy of the reproducer to determine keystroke latency
Created attachment 674722 [details] Local copy of a reproducer to determine password length for "su -" session
Statement: This issue affects the versions of the Linux kernel as shipped with Red Hat Enterprise Linux 5 and 6, and Red Hat Enterprise MRG 2. Red Hat Product Security has rated this issue as having Low security impact. This issue is not currently planned to be addressed in future updates. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/