An Indian researcher discovered an important local privilege escalation vulnerability that poses a security threat to most
Linux distros and BSD variants. Exploiting the bug in the X.Org server could allow an attacker to gain root access.
Vulnerability In X.Org Server Discovered
Researcher
Narendra Shinde
discovered a serious vulnerability affecting multiple BSD and Linux
distributions. Reportedly, X-Org server has local privilege escalation
flaw that allows an attacker to elevate privileges and gain root access.
Shinde has disclosed his findings in a separate
report.
As stated, the x-Org server has an “arbitrary file overwrite”
vulnerability. It allows an attacker to create or amend files on the
target system.
“X.org X Server application is vulnerable to privilege
escalation issue. X.org X Server application allows lower privileged
user to create or overwrite file anywhere on system, including files
owned by privileged users (ex. /etc/shadow). The attacker needs to have
active console session to exploit this issue.”
According to
X.org’s security advisory,
the vulnerability mainly exists due to incorrect handling and
validation of argument for at least two command-line parameters:
-modulepath, and –logfile.
“Incorrect command-line parameter validation in the Xorg X
server can lead to privilege elevation and/or arbitrary files
overwrite, when the X server is running with elevated privileges (ie
when Xorg is installed with the setuid bit set and started by a non-root
user).”
Although, the vulnerability won’t let an attacker gain access to the
system, it certainly facilitates them to gain complete control if they
already have a lower privileged account. The issue received
CVE-2018-14665, and mainly affects X.Org X server 1.19.0 and later.
Another researcher Matthew Hickey of the Hacker House has also shared his POC in a tweet.
X.Org Patched The Bug
X.Org server is a core graphics and windowing technology that
provides the base for GNOME and KDE desktop interface suites. It forms a
major component of most Linux distros and BSD variants that offer a GUI
interface.
X.Org explained:
“The -modulepath argument can be used to specify an
insecure path to modules that are going to be loaded in the X server,
allowing to execute unprivileged code in the privileged process. The
-logfile argument can be used to overwrite arbitrary files in the file
system, due to incorrect checks in the parsing of the option.”
After the discovery of the vulnerability, Shinde informed X.Org and
Red Hat teams of the matter. Since then, both X.Org and Red Hat stepped
up to patch the bug. After that, the researcher published a coordinated
disclosure on October 25, 2018.
Users can find the patch for this vulnerability on the
xserver repository. If the patch isn’t available, then X.Org suggests a workaround.
“If a patched version of the X server is not available,
X.Org recommends to remove the setuid bit (ie chmod 755) of the
installed Xorg binary. Note that this can cause issues if people are
starting the X window system using the ‘startx’, ‘xinit’ commands or
variations thereof.”
In addition, the affected distros including
OpenBSD,
Red Hat,
Ubuntu,
Debian,
SUSE, CentOS, and Fedora have also published separate security advisories recommending the patches.
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