hacking

82 Articles

Thin Client Hack

Hacking A Thin Client To Gain Root Access

April 29, 2015 by 15 Comments

[Roberto] recently discovered a clever way to gain root access to an HP t520 thin client computer. These computers run HP’s ThinPro operating system. The OS is based on Linux and is basically just a lightweight system designed to boot into a virtual desktop image loaded from a server. [Roberto’s] discovery works on systems that are running in “kiosk mode”.

The setup for the attack is incredibly simple. The attacker first stops the virtual desktop image from loading. Then, the connection settings are edited. The host field is filled with garbage, which will prevent the connection from actually working properly. The real trick is in the “command line arguments” field. The attacker simply needs to add the argument “&& xterm”. When the connection is launched, it will first fail and then launch the xterm program. This gives the attacker a command shell running under the context of whichever user the original software is running as.

The next step is to escalate privileges to root. [Roberto] discovered a special command that the default user can run as root using sudo. The “”hpobl” command launches the HP Easy Setup Wizard. Once the wizard is opened, the attacker clicks on the “Thank You” link, which will then load up the HP website in a version of Firefox. The final step is to edit Firefox’s default email program association to xterm. Now when the attacker visits an address like “mailto:test@test.com”, Firefox (running as root) launches xterm with full root privileges. These types of attacks are nothing new, but it’s interesting to see that they still persist even in newer software.

Race Conditions Exploit Granted Free Money On Web Services

April 29, 2015 by 10 Comments

[Josip] has been playing around with race conditions on web interfaces lately, finding vulnerabilities on both Facebook and Digital Ocean. A race condition can occur when a piece of software processes multiple threads using a shared resource.

For example, [Josip] discovered that he was able to manipulate page reviews using just a single Facebook account. Normally, a user is permitted to leave just one review for any given Facebook page. This prevents a single user from being able to skew the page’s overall ranking by making a bunch of positive or negative reviews. The trick to manipulating the system was to intercept the HTTP request that submitted the page review. The request was then replayed over and over in a very short amount of time.

Facebook’s servers ended up processing some of these requests simultaneously, essentially unaware that multiple requests had come in so close together. The result was that multiple reviews were submitted, artificially changing the pages overall ranking even though only one review actually showed up on the page for this user. The user can then delete their single review, and repeat this cycle over and over. It took Facebook approximately two months to fix this vulnerability, but in the end it was fixed and [Josip] received a nice bounty.

The Digital Ocean hack was essentially the exact same process. This time instead of hacking page reviews, [Josip] went after some free money. He found that he was able to submit the same promotional code multiple times, resulting in a hefty discount at checkout time. Digital Ocean wasted no time fixing this bug, repairing it within just ten days of the disclosure.

Screensaver Hack

Bypassing The Windows Lock Screen

February 28, 2015 by 87 Comments

Most of us know that we should lock our computers when we step away from them. This will prevent any unauthorized users from gaining access to our files. Most companies have some sort of policy in regards to this, and many even automatically lock the screen after a set amount of time with no activity. In some cases, the computers are configured to lock and display a screen saver. In these cases, it may be possible for a local attacker to bypass the lock screen.

[Adrian] explains that the screen saver is configured via a registry key. The key contains the path to a .scr file, which will be played by the Adobe Flash Player when the screen saver is activated. When the victim locks their screen and steps away from the computer, an attacker can swoop in and defeat the lock screen with a few mouse clicks.

First the attacker will right-click anywhere on the screen. This opens a small menu. The attacker can then choose the “Global settings” menu option. From there, the attacker will click on “Advanced – Trusted Location Settings – Add – Add File”. This opens up the standard windows “Open” dialog that allows you to choose a file. All that is required at this point is to right-click on any folder and choose “Open in a new window”. This causes the folder to be opened in a normal Windows Explorer window, and from there it’s game over. This window can be used to open files and execute programs, all while the screen is still locked.

[Adrian] explains that the only remediation method he knows of is to modify the code in the .swf file to disable the right-click menu. The only other option is to completely disable the flash screen saver. This may be the safest option since the screen saver is most likely unnecessary.

Update: Thanks [Ryan] for pointing out some mistakes in our post. This exploit specifically targets screensavers that are flash-based, compiled into a .exe file, and then renamed with the .scr extension. The OP mentions these are most often used in corporate environments. The exploit doesn’t exist in the stock screensaver.

Uber Hack

Stumbling Upon An Uber Vulnerability

February 27, 2015 by 30 Comments

[Nathan] is a mobile application developer. He was recently debugging one of his new applications when he stumbled into an interesting security vulnerability while running a program called Charles. Charles is a web proxy that allows you to monitor and analyze the web traffic between your computer and the Internet. The program essentially acts as a man in the middle, allowing you to view all of the request and response data and usually giving you the ability to manipulate it.

While debugging his app, [Nathan] realized he was going to need a ride soon. After opening up the Uber app, he it occurred to him that he was still inspecting this traffic. He decided to poke around and see if he could find anything interesting. Communication from the Uber app to the Uber data center is done via HTTPS. This means that it’s encrypted to protect your information. However, if you are trying to inspect your own traffic you can use Charles to sign your own SSL certificate and decrypt all the information. That’s exactly what [Nathan] did. He doesn’t mention it in his blog post, but we have to wonder if the Uber app warned him of the invalid SSL certificate. If not, this could pose a privacy issue for other users if someone were to perform a man in the middle attack on an unsuspecting victim.

[Nathan] poked around the various requests until he saw something intriguing. There was one repeated request that is used by Uber to “receive and communicate rider location, driver availability, application configurations settings and more”. He noticed that within this request, there is a variable called “isAdmin” and it was set to false. [Nathan] used Charles to intercept this request and change the value to true. He wasn’t sure that it would do anything, but sure enough this unlocked some new features normally only accessible to Uber employees. We’re not exactly sure what these features are good for, but obviously they aren’t meant to be used by just anybody.

Facebook Bounty

Deleting Facebook Albums Without Permission

February 15, 2015 by 17 Comments

[Laxman] was poking around Facebook looking for security vulnerabilities. Facebook runs a bug bounty program which means if you can find a vulnerability that’s serious enough, it can earn you cold hard cash. It didn’t take much for [Laxman] to find one worthy of a bounty.

The graph API is the primary way for Facebook apps to read and write to the Facebook social graph. Many apps use this API, but there are limitations to what it can do. For example, the API is unable to delete users’ photo albums. At least, it’s not supposed to be able too. [Laxman] decided to test this claim himself.

He started by sending a command to delete one of his own albums using a graph explorer access token. His request was denied. The application didn’t have the correct permissions to be able to perform that action. It seemed that Facebook was correct and the API was unable to delete photos. [Laxman] had another trick up his sleeve, though. He noticed that the wording of the response suggested that other apps would have the ability to delete the albums, so he decided to check the Facebook mobile application.

He decided to send the same request with a different token. This time he used a token from the Facebook for Mobile application. This actually worked, and resulted in his photo album being deleted. To take things a step further, [Laxman] sent the same requests, but changed the user’s ID to a victim account he had set up. The request was accepted and processed without a problem. This meant that [Laxman] could effectively delete photo albums from any other user without that user’s consent. The vulnerability did require that [Laxman] had permission to view the album in the first place.

Since [Laxman] is one of the good guys, he sent this bug in to the Facebook team. It took them less than a day to fix the issue and they rewarded [Laxman] $12,500 for his trouble. It’s always nice to be appreciated. The video below shows [Laxman] walking through how he pulled off this hack using Burp Suite. Continue reading “Deleting Facebook Albums Without Permission” →

Using HID Tricks To Drop Malicious Files

January 27, 2015 by 38 Comments

[Nikhil] has been experimenting with human interface devices (HID) in relation to security. We’ve seen in the past how HID can be exploited using inexpensive equipment. [Nikhil] has built his own simple device to drop malicious files onto target computers using HID technology.

The system runs on a Teensy 3.0. The Teensy is like a very small version of Arduino that has built-in functionality for emulating human interface devices, such as keyboards. This means that you can trick a computer into believing the Teensy is a keyboard. The computer will treat it as such, and the Teensy can enter keystrokes into the computer as though it were a human typing them. You can see how this might be a security problem.

[Nikhil’s] device uses a very simple trick to install files on a target machine. It simply opens up Powershell and runs a one-liner command. Generally, this commend will create a file based on input received from a web site controlled by the attacker. The script might download a trojan virus, or it might create a shortcut on the user’s desktop which will run a malicious script. The device can also create hot keys that will run a specific script every time the user presses that key.

Protecting from this type off attack can be difficult. Your primary option would be to strictly control USB devices, but this can be difficult to manage, especially in large organizations. Web filtering would also help in this specific case, since the attack relies on downloading files from the web. Your best bet might be to train users to not plug in any old USB device they find lying around. Regardless of the methodology, it’s important to know that this stuff is out there in the wild.

Inventory Report

Security Problems With Gas Station Automated Tank Gauges

January 22, 2015 by 29 Comments

[HD Moore] recently posted an article on Rapid 7’s blog about an interesting security problem. They’ve been doing some research into the security of automated tank gauges (ATGs). These devices are used at gas stations and perform various functions including monitoring fuel levels, tracking deliveries, or raising alarms. [Moore] says that ATGs are used at nearly every fueling station in the United States, but they are also used internationally. It turns out these things are often not secured properly.

Many ATG’s have a built-in serial port for programming and monitoring. Some systems also have a TCP/IP card, or even a serial to TCP/IP adapter. These cards allow technicians to monitor the system remotely. The most common TCP port used in these systems is port 10001. Some of these systems have the ability to be password protected, but Rapid 7’s findings indicate that many of them are left wide open.

The vulnerability was initial reported to Rapid 7 by [Jack Chadowitz]. He discovered the problem due to his work within the industry and developed his own web portal to help people test their own systems. [Jack] approached Rapid 7 for assistance in investigating the issue on a much larger scale.

Rapid 7 then scanned every IPv4 address looking for systems with an open port 10001. Each live system discovered was then sent a “Get In-Tank Inventory Report” request. Any system vulnerable to attack would respond with the station name, address, number of tanks, and fuel types. The scan found approximately 5,800 systems online with no password set. Over 5,300 of these stations are in the United States.

Rapid 7 believes that attackers may be able to perform such functions as to reconfigure alarm thresholds, reset the system, or otherwise disrupt operation of the fuel tank. An attacker might be able to simulate false conditions that would shut down the fuel tank, making it unavailable for use. Rapid 7 does not believe this vulnerability is actively being exploited in the wild, but they caution that it would be difficult to tell the difference between an attack and a system failure. They recommend companies hide their systems behind a VPN for an additional layer of security.

[Thanks Ellery]