New Privilege Escalation Flaw Affects Most Linux Distributions

Oct 26, 2018

An Indian security researcher has discovered a highly critical
flaw in X.Org Server package that impacts OpenBSD and most
Linux distributions, including Debian, Ubuntu, CentOS, Red Hat, and
Fedora.

Xorg X server is a popular open-source implementation of the X11
system (display server) that offers a graphical environment to a
wider range of hardware and OS platforms. It serves as an
intermediary between client and user applications to manage
graphical displays.

According to a blog post
published by software security engineer Narendra Shinde,
Xorg X server doesn’t correctly handle and validate arguments for
at least two command-line parameters, allowing a low-privileged
user to execute malicious code and overwrite any file—including
files owned by privileged users like root.
^[1]

The flaw, tracked as CVE-2018-14665, was introduced in X.Org
server 1.19.0 package that remained undetected for almost two years
and could have been exploited by a local attacker on the terminal
or via SSH to elevate their privileges on a target system.

The two vulnerable parameters in question are:

-modulepath: to set a directory path to search for Xorg
server modules,
-logfile: to set a new log file for the Xorg server,
instead of using the default log file that is located at
/var/log/Xorg.n.log on most platforms.

“When the X server is running with elevated privileges (i.e., when
Xorg is installed with the setuid bit set and started by a non-root
user).” the Xorg advisory ^[2] says. “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.”

“An incorrect permission check for -modulepath and -logfile options
when starting Xorg X server allows unprivileged users with the
ability to log in to the system via physical console to escalate
their privileges and run arbitrary code under root privileges.”
Red Hat ^[3]
advisory says.

Security researcher Matthew Hickey shared an easy to execute
proof-of-concept ^[4]
exploit code earlier today on Twitter, saying ^[5] “An attacker can
literally take over impacted systems with 3 commands or
less.”

The X.Org foundation has now released X.Org Server version 1.20.3
with security patches to address the issue.

Popular distributions like OpenBSD,
Debian, Ubuntu, CentOS,
Red Hat, and Fedora have published their advisories to confirm the
issue and working on the patch updates.
^[6]^[7]^[8]

References

^{^}
blog post
(www.securepatterns.com)
^{^}
advisory
(lists.x.org)
^{^}
Red Hat
(bugzilla.redhat.com)
^{^}
proof-of-concept
(twitter.com)
^{^}
saying
(twitter.com)
^{^}
OpenBSD
(ftp.openbsd.org)
^{^}
Debian
(security-tracker.debian.org)
^{^}
Ubuntu
(people.canonical.com)

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OWASP TOP !0

Injection. Injection flaws, such as SQL, NoSQL, OS, and LDAP injection, occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s hostile data can trick the interpreter into executing unintended commands or accessing data without proper authorization. Broken Authentication. Application functions related to authentication and session management are often implemented incorrectly, allowing attackers to compromise passwords, keys, or session tokens, or to exploit other implementation flaws to assume other users’ identities temporarily or permanently. Sensitive Data Exposure. Many web applications and APIs do not properly protect sensitive data, such as financial, healthcare, and PII. Attackers may steal or modify such weakly protected data to conduct credit card fraud, identity theft, or other crimes. Sensitive data may be compromised without extra protection, such as encryption at rest or in transit, and requires special precautions when exchanged with the browser. XML External Entities (XXE). Many older or poorly configured XML processors evaluate external entity references within XML documents. External entities can be used to disclose internal files using the file URI handler, internal file shares, internal port scanning, remote code execution, and denial of service attacks. Broken Access Control. Restrictions on what authenticated users are allowed to do are often not properly enforced. Attackers can exploit these flaws to access unauthorized functionality and/or data, such as access other users’ accounts, view sensitive files, modify other users’ data, change access rights, etc. Security Misconfiguration. Security misconfiguration is the most commonly seen issue. This is commonly a result of insecure default configurations, incomplete or ad hoc configurations, open cloud storage, misconfigured HTTP headers, and verbose error messages containing sensitive information. Not only must all operating systems, frameworks, libraries, and applications be securely configured, but they must be patched/upgraded in a timely fashion. Cross-Site Scripting XSS. XSS flaws occur whenever an application includes untrusted data in a new web page without proper validation or escaping, or updates an existing web page with user-supplied data using a browser API that can create HTML or JavaScript. XSS allows attackers to execute scripts in the victim’s browser which can hijack user sessions, deface web sites, or redirect the user to malicious sites. Insecure Deserialization. Insecure deserialization often leads to remote code execution. Even if deserialization flaws do not result in remote code execution, they can be used to perform attacks, including replay attacks, injection attacks, and privilege escalation attacks. Using Components with Known Vulnerabilities. Components, such as libraries, frameworks, and other software modules, run with the same privileges as the application. If a vulnerable component is exploited, such an attack can facilitate serious data loss or server takeover. Applications and APIs using components with known vulnerabilities may undermine application defenses and enable various attacks and impacts. Insufficient Logging & Monitoring. Insufficient logging and monitoring, coupled with missing or ineffective integration with incident response, allows attackers to further attack systems, maintain persistence, pivot to more systems, and tamper, extract, or destroy data. Most breach studies show time to detect a breach is over 200 days, typically detected by external parties rather than internal processes or monitoring.

New Privilege Escalation Flaw Affects Most Linux Distributions

References

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