Original release date: September 25, 2014

Systems Affected

• GNU Bash through 4.3.
• Linux, BSD, and UNIX distributions including but not limited to:
  • CentOS 5 through 7
  • Debian
  • Mac OS X
  • Red Hat Enterprise Linux 4 through 7
  • Ubuntu 10.04 LTS, 12.04 LTS, and 14.04 LTS

Overview

A critical vulnerability has been reported in the GNU Bourne Again Shell (Bash), the common command-line shell used in most Linux/UNIX operating systems and Apple’s Mac OS X. The flaw could allow an attacker to remotely execute shell commands by attaching malicious code in environment variables used by the operating system [1]. The United States Department of Homeland Security (DHS) is releasing this Technical Alert to provide further information about the GNU Bash vulnerability.

Description

GNU Bash versions 1.14 through 4.3 contain a flaw that processes commands placed after function definitions in the added environment variable, allowing remote attackers to execute arbitrary code via a crafted environment which enables network-based exploitation. [2, 3]

Critical instances where the vulnerability may be exposed include: [4, 5]

• Apache HTTP Server using mod_cgi or mod_cgid scripts either written in bash, or spawn subshells.
• Override or Bypass ForceCommand feature in OpenSSH sshd and limited protection for some Git and Subversion deployments used to restrict shells and allows arbitrary command execution capabilities.
• Allow arbitrary commands to run on a DHCP client machine, various Daemons and SUID/privileged programs.
• Exploit servers and other Unix and Linux devices via Web requests, secure shell, telnet sessions, or other programs that use Bash to execute scripts.

Impact

This vulnerability is classified by industry standards as “High” impact with CVSS Impact Subscore 10 and “Low” on complexity, which means it takes little skill to perform. This flaw allows attackers to provide specially crafted environment variables containing arbitrary commands that can be executed on vulnerable systems. It is especially dangerous because of the prevalent use of the Bash shell and its ability to be called by an application in numerous ways.

Solution

Patches have been released to fix this vulnerability by major Linux vendors for affected versions. Solutions for CVE-2014-6271 do not completely resolve the vulnerability. It is advised to install existing patches and pay attention for updated patches to address CVE-2014-7169.

Many UNIX-like operating systems, including Linux distributions, BSD variants, and Apple Mac OS X include Bash and are likely to be affected. Contact your vendor for updated information. A list of vendors can be found in CERT Vulnerability Note VU#252743 [6].

US-CERT recommends system administrators review the vendor patches and the NIST Vulnerability Summary for CVE-2014-7169, to mitigate damage caused by the exploit.

References

• Ars Technica, Bug in Bash shell creates big security hole on anything with *nix in it;
• DHS NCSD; Vulnerability Summary for CVE-2014-6271
• DHS NCSD; Vulnerability Summary for CVE-2014-7169
• Red Hat, CVE-2014-6271
• Red Hat, Bash specially-crafted environment variables code injection attack
• CERT Vulnerability Note VU#252743

Revision History

• September 25, 2014 – Initial Release

This product is provided subject to this Notification and this Privacy & Use policy.

Tor is a network of virtual tunnels that allows people and groups to improve their privacy and security on the Internet. It also enables software developers to create new communication tools with built-in privacy features. It provides the foundation for a range of applications that allow organizations and individuals to share information over public networks without compromising their privacy. Individuals can use it to keep remote Websites from tracking them and their family members. They can also use it to connect to resources such as news sites or instant messaging services that are blocked by their local Internet service providers (ISPs).

This abuses the bug in bash environment variables (CVE-2014-6271) to get a suid binary inside of VMWare Fusion to launch our payload as root.

LibVNCServer versions 0.9.9 and below suffer from memory management handling, buffer overflow, and denial of service vulnerabilities.

Cisco Security Advisory – A vulnerability in the Network Address Translation (NAT) feature of Cisco IOS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to improper translation of IP version 4 (IPv4) packets. Cisco has released free software updates that address this vulnerability.

A stack overflow was discovered when serializing data via the Data::Dumper extension which is part of Perl-Core. By using the “Dumper” method on a large Array-Reference which recursively contains other Array-References, it is possible to cause many recursive calls to the DD_dump native function and ultimately exhaust all available stack memory.