Linux

Hacking Skills Challenge - Level 7

Once again it’s a slow security news week, so time to tackle the next hacking skills challenge level. So far, we’ve explored the first 6 basic missions at HackThisSite.org. The difficulty level is supposed to increase at each level, but this one is only difficult if you don’t know Linux. Here’s the challenge:

The password is hidden in an unknown file, and Sam has set up a script to display a calendar. Requirements: Basic UNIX command knowledge.

This time Network Security Sam has saved the unencrypted level7 password in an obscurely named file saved in this very directory.

In other unrelated news, Sam has set up a script that returns the output from the UNIX cal command.

This one is so easy you don’t even have to look at the source code. But you do have to know about chaining commands in Unix.

If you enter a year, you’ll get a full 12-month calendar with all weeks beginning on Sunday displayed on the resulting output page. This is default behavior of the cal command. It looks like all the script does is execute the command, taking your input as a parameter.  We can prove this by leaving the field blank; the script returns the current month and year, i.e., default behavior.

The key to cracking this one is the phrase “…obscurely named file saved in this very directory.” We know the permissions are good to run commands on that directory, so let’s just chain the ls — list directory contents — command and see what happens. (You chain commands in Linux using && between them.) Enter the following in the text box: && ls and click the View button. Here’s the output:

       October 2009
Mon Tue Wed Thu Fri Sat Sun
              1   2   3   4
  5   6   7   8   9  10  11
 12  13  14  15  16  17  18
 19  20  21  22  23  24  25
 26  27  28  29  30  31

.
..
level7.php
cal.pl

index.php
k1kh31b1n55h.php
perl5.8.9.core

Looks to me like k1kh31b1n55h.php is our file. Stick it in the URL and open it up. Voila! The password, f866d6b9, is revealed.

Mission accomplished!

Protecting Your Business from Online Banking Fraud

I’m pleased to see some professionals with clout advocating a security practice I have often recommended to my clients. Brian Krebs of The Washington Post and SANS Institute are both pushing the use of Linux live CDs for online banking. Krebs’ latest article, “Avoid Windows Malware: Bank on a Live CD,” starts off by recommending people NOT use Microsoft Windows for online banking:

An investigative series I’ve been writing about organized cyber crime gangs stealing millions of dollars from small to mid-sized businesses has generated more than a few responses from business owners who were concerned about how best to protect themselves from this type of fraud.

The simplest, most cost-effective answer I know of? Don’t use Microsoft Windows when accessing your bank account online.

Krebs has reported frequently about some of the more prominent online banking fraud incidents, including the hack against Bullitt County, Ky. and two California firms that lost a combined total of more than half a million dollars, both of which were using two-factor authentication requiring the use of a security token.

The credential-stealing Trojans used in these attacks were designed to avoid detection by normal anti-malware software, so the victims had no clues that they had been infected. With the huge amounts of money involved, it’s likely the cybercriminals have evolved their programming skills to the point where it will be difficult for security firms to keep up.

It’s not surprising, then, that SANS, as a direct result of Krebs’ reporting, issued a challenge to its students to create a white paper to determine the most effective methods for small and mid-sized businesses to mitigate the threat from these types of attacks. The report, “Protecting Your Business from Online Banking Fraud,” addresses the issue. Here’s that report’s Abstract:

Recently, small and medium businesses have lost millions of dollars from fraudulent electronic financial transactions.  This paper reviews the threat and provides guidance for mitigating the threat.  These crimes typically begin with a phishing email targeted at the comptroller or other staff in the finance department.  After the comptroller’s computer is compromised, sophisticated malware is used to eavesdrop on the comptroller’s activity and account credentials for financial systems.  Once the attackers have the required information, they begin to steal money with fraudulent transactions in amounts below $10,000.  These smaller amounts fly under the laundering detection mechanisms in the US Bank Secrecy Act.  In many cases, repeated transactions have added up to hundreds of thousands of dollars lost by individual organizations.  The paper provides a number of possible ways to mitigate these types of attacks.  A defense in depth approach is used to provide multiple mitigation recommendations.  The number one recommended mitigation is to use a read-only bootable alternative media (ROBAM) as an isolated environment for financial transactions. [emphasis added] The mitigation steps also include protecting the email address of the comptroller, network protection, endpoint protection, virtual machines, awareness training, policy changes and monitoring financial transactions.

I highly recommend that everyone responsible for security in their organization read this paper.

Is Linux Security as Bad as Microsoft Windows “Security?”

Linux proponents often gloat over the seeming lack of security vulnerabilities in the Linux kernel when compared to Microsoft Windows; Windows proponents counter saying that Linux is just enjoying “security through obscurity.” Seems the Windows people may be justified to some degree as reports of a Linux vulnerability puts most versions of the Linux kernel built in the last eight years at risk of complete takeover.

According to The Register, “The bug involves the way kernel-level routines such as sock_sendpage react when they are left unimplemented. Instead of linking to a corresponding placeholder, (for example, sock_no_accept), the function pointer is left uninitialized. Sock_sendpage doesn’t always validate the pointer before dereferencing it, leaving the OS open to local privilege escalation that can completely compromise the underlying machine.” This means that it’s trivial for an attacker to put code in the first page and that code will get executed with kernel privileges. You can read a full rundown of the vulnerability at the CR0 Blog.

All Linux kernel 2.4 and 2.6 versions since May 2001 are affected. The vulnerability has been patched, but “this is the second time in less than a month that a serious security vulnerability has been reported in the Linux kernel. In mid July, a researcher alerted Linux developers to a separate "NULL pointer dereference" bug that put newer versions at risk of complete compromise,” according to The Register.

There’s no question that Microsoft has ongoing security issues; it’s no surprise that Linux is beginning to show the same. The only difference lies in the attack surface; Microsoft is still the biggest target. As Linux continues to gain market share, however, we’ll be seeing more researchers focusing their attention on the Open Source OS; as they do, they’ll find more and more vulnerabilities there, too.

There’s a technology called “secure coding” that still hasn’t been fully developed, much less implemented on a grand scale; until programmers fully get this concept, we’re saddled with insecure OS’s and applications.

Are Windows PCs Threatened by Malware Harbored on Mac & Linux OS’s?

Can Mac and Linux boxes harbor malware that does not affect them, but could affect Windows PCs?  Absolutely. It can and does happen. The Sophos white paper, “Protecting Mac and Linux computers: genuine need or nice to have?” presents a convincing case, describing just how Mac and UNIX/Linux machines threaten Windows PCs.

…it is very common for Windows networks to include a server running UNIX or Linux. Vulnerabilities, such as a weak SSH password, can allow hackers to convert a Linux server into a botnet controller, and install malware that will compromise desktop Windows computers.

Well, that’s one way, but consider this: Viruses, worms, and other types of malware are files, and can be stored on any digital media, regardless of the format or operating system that created them. A Mac/UNIX/Linux machine can store Windows files; a Windows machine can store Mac/UNIX/Linux files. That a Windows virus cannot damage a Mac/UNIX/Linux machine–and vice-versa–is irrelevant: Typhoid Mary harbored and transmitted typhoid fever yet never succumbed to it. She did, however, infect 47 others, three of whom died.

…computers harboring the malware can quietly transmit it to Windows computers. For example, UNIX computers can easily transmit the virus to Windows computers via the Samba fle-sharing system.

If you have a mixed network, it’s time to put some effort into protecting the non-Windows machines. Best practice now dictates that every server and desktop machine in your network be protected with some sort of anti-malware application.

Bootable Thumb Drive Virus Scanner Saves the Day

Forgive me if I brag a bit in this post, but I think I earned the right. You be the judge.

Last weekend, I noticed strange behavior on my home system. ESET Smart Security kept reporting that it had “found and quarantined m.exe, probably a variant of Win.Qhost trojan.” Every time I plugged in a USB thumb drive, ESET would pop up with the message. I couldn’t run HijackThis. If I tried to go to certain antivirus websites–Avira in particular–my browser closed. Sysinternals Process Explorer wouldn’t run. My thumb drive showed two hidden files: Autorun.inf and m.exe. Hmmm. Running ipconfig /displaydns revealed multiple connections to porn and malware sites. Searching Google led me to some tools that eventually fixed my problem at home. Turns out I had a bigger problem.

Apparently, I had picked up the infection from a client’s Exchange server and during my weekly tour there, I found that the tools I used on my XP machine wouldn’t run on Windows Server 2003.  I tried everything in my arsenal; no tool found anything wrong. This thing was very stealthy; even Safe Mode didn’t disable it. I was about to give up. Then I remembered that I’d recently finished making up a bootable Linux thumb drive virus scanner using the AntiVir rescue CD, a tool that allows offline scanning (thank you, Avira, you made it a little easier for me). I booted the server to the thumb drive, ran the scan, rebooted the server, and voila! The infection was gone.

There’s a whole backstory to this incident that I won’t bore you with. Suffice it to say that I’m glad I put in the hours of hacking and research to come up with a really useful tool that I was able to use to help a client. Veni! Vidi! Vici!

CERT Says Linux is Under Attack

It had to happen sooner or later; as Linux gains an ever-increasing foothold (Linux market share to reach 7% in 2008 ) in the market, it will become a viable target for criminal hackers. According to the U.S. Computer Emergency Readiness Team (CERT) in US-CERT Current Activity, attacks are already underway:

US-CERT is aware of active attacks against linux-based computing infrastructures using compromised SSH keys. The attack appears to initially use stolen SSH keys to gain access to a system, and then uses local kernel exploits to gain root access. Once root access has been obtained, a rootkit known as “phalanx2″ is installed.

Phalanx2 appears to be a derivative of an older rootkit named “phalanx”. Phalanx2 and the support scripts within the rootkit, are configured to systematically steal SSH keys from the compromised system. These SSH keys are sent to the attackers, who then use them to try to compromise other sites and other systems of interest at the attacked site.

For now, the attack is easily detected (though variants of the rootkit will likely change its behavior): The attack creates a directory “/etc/khubd.p2/” that is hidden from “ls,” but it can be entered with “cd /etc/khubd.p2″. Any directory named “khubd.p2,” regardless of its location, is hidden from “ls” but can be entered using “cd.” Additionally, “/dev/shm/” may contain files from the attack, so anything unusual in there is suspect. You can also try searching for hidden processes and checking the reference count in “/etc” against the number of directories shown by “ls”.

Check out the full article, “SSH Key-based Attacks” for complete details on risk mitigation and compromise response.

Two Ways to Operate Securely on the Web

If you’ve done any coding at all, you probably have a good idea why software developers often run their untested code in a protected environment–a sandbox. If the software misbehaves, all you have to do is shut down the sandbox and everything returns to normal, no harm done.

A sandbox is also a great way to prevent viruses and other malware from infecting your machine while browsing the web. Confine your browser to its own little box and if any malicious software tries to run, it can’t get to your system, it stays within in the box’s boundaries. Kill the box and you kill the malware. The top, free sandbox program for Windows–the one I use for secure surfing and testing– is Sandboxie. It runs only on Windows and is Vista-compatible. Run Internet Explorer, Firefox, or any other program under Sandboxie and you should be safe.

Flash Update: Seems CheckPoint agrees and has released a product of its own. Check out this article from Dark Reading.

You can also operate securely from inside a virtual machine. This is different from a sandbox in that you actually run an entire operating system, rather than a single program. Many people, this Geek included, use virtual machines to run alternative operating systems like Linux. In a virtual machine, you can do everything you do on a real machine and like the sandbox, if things go wrong, your computer won’t be harmed. A big advantage of the virtual machine over a sandbox is that you can examine the actual behavior of malware and any damage to the OS. Microsoft provides the free Virtual PC and VMware provides its free VMware Player and VMware Server. For the Mac, there’s Parallels (not free). You might want to check out the secure browsing applicance provided for VMware Player.

Security Maxim #9:

When surfing the web, testing unknown programs, or engaging in other activities with the potential to harm your computer, use a sandbox or virtual machine to protect your base system from harm.