Linux admins need to get busy patching, as a newly discovered bug has emerged in the kernel's tty handling – and it lets logged-in users crash the system, gain root privileges, or otherwise modify and access data they shouldn't.
This memory corruption flaw is certainly nothing like OpenSSL's remotely exploitable Heartbleed – CVE-2014-0196. But this local root hole is problematic where users are sharing the same Linux host in the cloud.
Here's how US-CERT described the issue:
“The n_tty_write function in drivers/tty/n_tty.c in the Linux kernel through 3.14.3 does not properly manage tty driver access in the 'LECHO & !OPOST' case, which allows local users to cause a denial of service (memory corruption and system crash) or gain privileges by triggering a race condition involving read and write operations with long strings.”
A user only needs shell access to be in a position to exploit the programming blunder.
The bug was introduced in 2009 with version v2.6.31-rc3 of the kernel. Before that, as noted at this Novell SUSE security discussion, “pty [the pseudo-terminal – El Reg] was writing directly to a line discipline without using buffers”.
Ubuntu has been patched, Red Hat is working on a fix for its Enterprise Linux 6 and Enterprise MRG 2 distos (RH Enterprise Linux 5 isn't affected). OpenWall has also patched. Debian's patches will arrive here.
There's an unreliable proof-of-concept here. ®