Linux security alert: Bug in sudo’s get_process_ttyname() [ CVE-2017-1000367 ]
There is a serious vulnerability in sudo command that grants root access to anyone with a shell account. It works on SELinux enabled systems such as CentOS/RHEL and others too. A local user with privileges to execute commands via sudo could use this flaw to escalate their privileges to root. Patch your system as soon as possible.
It was discovered that Sudo did not properly parse the contents of /proc/[pid]/stat when attempting to determine its controlling tty. A local attacker in some configurations could possibly use this to overwrite any file on the filesystem, bypassing intended permissions or gain root shell.
From the description:
We discovered a vulnerability in Sudo’s get_process_ttyname() for Linux:
this function opens “/proc/[pid]/stat” (man proc) and reads the device number of the tty from field 7 (tty_nr). Unfortunately, these fields are space-separated and field 2 (comm, the filename of the command) can
contain spaces (CVE-2017-1000367).
For example, if we execute Sudo through the symlink “./ 1 “, get_process_ttyname() calls sudo_ttyname_dev() to search for the non-existent tty device number “1” in the built-in search_devs.
Next, sudo_ttyname_dev() calls the function sudo_ttyname_scan() to search for this non-existent tty device number “1” in a breadth-first traversal of “/dev”.
Last, we exploit this function during its traversal of the world-writable “/dev/shm”: through this vulnerability, a local user can pretend that his tty is any character device on the filesystem, and
after two race conditions, he can pretend that his tty is any file on the filesystem.
On an SELinux-enabled system, if a user is Sudoer for a command that does not grant him full root privileges, he can overwrite any file on the filesystem (including root-owned files) with his command’s output,
because relabel_tty() (in src/selinux.c) calls open(O_RDWR|O_NONBLOCK) on his tty and dup2()s it to the command’s stdin, stdout, and stderr. This allows any Sudoer user to obtain full root privileges.
A list of affected Linux distro
- Red Hat Enterprise Linux 6 (sudo)
- Red Hat Enterprise Linux 7 (sudo)
- Red Hat Enterprise Linux Server (v. 5 ELS) (sudo)
- Oracle Enterprise Linux 6
- Oracle Enterprise Linux 7
- Oracle Enterprise Linux Server 5
- CentOS Linux 6 (sudo)
- CentOS Linux 7 (sudo)
- Debian wheezy
- Debian jessie
- Debian stretch
- Debian sid
- Ubuntu 17.04
- Ubuntu 16.10
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS
- SUSE Linux Enterprise Software Development Kit 12-SP2
- SUSE Linux Enterprise Server for Raspberry Pi 12-SP2
- SUSE Linux Enterprise Server 12-SP2
- SUSE Linux Enterprise Desktop 12-SP2
- OpenSuse, Slackware, and Gentoo Linux
How do I patch sudo on Debian/Ubuntu Linux server?
How do I patch sudo on CentOS/RHEL/Scientific/Oracle Linux server?
Run yum command:
$ sudo yum update
How do I patch sudo on Fedora Linux server?
Run dnf command:
$ sudo dnf update
How do I patch sudo on Suse/OpenSUSE Linux server?
Run zypper command:
$ sudo zypper update
How do I patch sudo on Arch Linux server?
Run pacman command:
$ sudo pacman -Syu
How do I patch sudo on Alpine Linux server?
Run apk command:
# apk update && apk upgrade
How do I patch sudo on Slackware Linux server?
Run upgradepkg command:
# upgradepkg sudo-1.8.20p1-i586-1_slack14.2.txz
How do I patch sudo on Gentoo Linux server?
Run emerge command:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-admin/sudo-1.8.20_p1"
For more information visit Bug report: Potential overwrite of arbitrary files on Linux.