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New tool tries to close master-key security vulnerability in Android

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July 17, 2013

There's now a new tool available that attempts to close the master-key security vulnerability in the Google Android operating system that allows malicious software to masquerade as legitimate mobile apps when they're not.

Free utility ReKey simply integrates into the underlying operating system to defend users who are concerned about exactly when an official security patch will arrive from their smartphone manufacturer or wireless carrier.

The so-called master-key vulnerability discovered by Bluebox Security affects nearly all Android devices. It allows hackers to take over Android devices by tricking users into installing rogue apps that carry the same digital signatures as legitimate applications.

The security issue stems from the ability to integrate files with the same filename inside Android application installer bundles.

The free operating system's cryptographic verifier validates the first version of any repeated file in an APK archive, but the installer extracts and deploys the lastest version, which could easily be a modified file with some nasty backdoor code built into it.

So a legitimate app could be hijacked to install malware on an Android device even though the system declares the downloaded unchanged and original.

A similar (although less potent) security vulnerability discovered by Chinese security researchers from Android Security Squad also allows attackers to smuggle untrusted code into Android application installer files.

The Chinese attack focuses on classes.dex APK files that are smaller than 64 Kb. By modifying an extra field length to 0xFFFD, it is possible to fool the integrity check and smuggle malicious code into an installation file, Kaspersky Lab's Threatpost reports.

Developed by mobile security firm Duo Security and Northeastern University's System Security Lab, ReKey is designed to stop both vulnerabilities without waiting for security updates from mobile carriers, which can take months or longer to arrive.

In mid-2012, Duo reported that more than 50 percent of Android devices globally have unpatched security vulnerabilities. With these recently disclosed security holes, that number will shoot up to 99 percent until wireless carriers are able to adequately patch their subscribers' devices.

Google has reportedly developed an Android update that addresses both the Bluebox master key vulnerability and the similar Chinese security flaws. Almost all Android devices today are vulnerable to the Bluebox master-key hole, since the vulnerability has existed since Android 1.6, but only the Samsung Galaxy S4 has been patched to protect against it, hence the need for a third-party fix like ReKey.

John Oberheide, CTO of Duo Security says that ReKey provided notification of attempted attacks featuring dodgy APKs as well as blocking the Bluebox master key and similar malware padding attacks.

"The app is powered by a Dalvik bytecode instrumentation framework," Oberheide explained. "In other words, we can reliably hook or interpose upon any code implemented in the Android framework, assuming we have sufficient privileges of course. To fix the master key hole, we hook the vulnerable routines in Android's package manager in order to block the attack vector."

"As a nice side effect of the hooking mechanism, we can detect when someone attempts to install a maliciously crafted APK, block it, and notify the user. Currently, the user will see a popup notifying them that an attempted attack took place," he added.

Years ago, security tool developers used to produce third-party fixes to defend against Windows zero-day vulnerabilities. Duo Security and computer scientists at Northeastern University have teamed up to do something similar to tackle this pressing Android security issue.

Oberheide, who agreed that the aforementioned comparison was apt, said that the ReKey application was low impact and could be left on devices even after an Android operating system update is applied.

"Determina and eEye used to release patches for critical Windows vulnerabilities before Microsoft got around to it," Oberheide said," he said.

"Since ReKey only patches in-memory and then re-patches upon boot of the device, it is non-destructive and makes no permanent changes to the user's device. When the official patch is delivered to the device, it can interoperate peacefully."

The ReKey app was released yesterday and is available to download at as well as through the Google Play Store.

"The security of Android devices globally is paralysed by the slow patching practices of mobile carriers and other parties in the Android ecosystem," Oberheide concluded.

"We are really excited to bring forward innovative technology like ReKey that places security controls back into the hands of users and enterprises," he added.

In other internet security news

Hackers have recently created an exceptionally nasty version of Mac malware that uses back-to-front trickery to disguise its true intentions.

Janicab, which is written in Python, takes advantage of the right-to-left U-202E Unicode character to mask the malicious file’s real extension.

The U-202E marker applies a right-to-left override for the display of part of the malware’s filename.

So a file which appears to be called RecentNews.ppa.pdf is actually The file is designed to trick users into thinking they are opening a .PDF file which is in reality an an executable .APP.

This sort of back-to-front trickery has been seen in Windows malware in the past - such as Bredolab and the high-profile Mahdi trojan from last year - but it's reckoned to be a new and unwelcome arrival on Macs.

In order to maintain the subterfuge, the malware displays a decoy document while silently executing in the background, installing malicious code on compromised Macs.

Because of the right-to-left override character, the usual file quarantine notification from OS X will also display with the words written backwards.

Adding an extra layer of sneakiness, the malware has been signed with an Apple Developer ID on top of all that.

That nasty file is designed to record audio and capture screenshots from infected computers, using the third-party command line utility SoX.

But wait, there's more. That information is then uploaded to a command-and-control server whose location is defined by pages on seemingly innocuous pages on YouTube.

A full description of the attack together with several screenshots can be found in a blog post by F-Secure, the Finnish anti-virus firm that was the first to issue a warning about the threat.

A good explanation of the right-to-left trickery that's the main feature of the malware can be found in a blog post by independent anti-virus expert Graham Cluley.

And a tip of the hat goes to David Hartley of Eset who described back-to-front mendaciousness as "Malice through the looking glass".

None of the antivirus experts have stuck their necks out on this point, but the amount of care taken to put together the malware gives us a clear idea of what hackers have been up to lately.

The decoy document dropped by Janicab is in Russian and that may well have something to do with the target audience.

In other internet security news

Servers powering the U.S. Emergency Alert System can be easily tricked into broadcasting bogus and apocalyptic warnings from far away, say internet security experts.

Scientists at computer security firm IO-Active say they found private encryption keys within firmware updates for the devices.

Armed with that information, miscreants could successfully remotely log into the servers, installed at television and radio stations around the United States, and as an administrator, they could broadcast panic-inducing messages to the mass media, creating wide-scale panic all over the nation.

The discovery comes just a few months after shortcomings in the U.S. Emergency Alert System (EAS) were exploited to beam news of a zombie apocalypse to American TVs.

Montana Television Network’s regular programming was interrupted by warnings of the end of the world back in February. Viewers of KRTC in Great Falls, Montana, were confronted by an on-air audio warning that "bodies of the dead are rising from their graves and attacking the living".

A scrolling text warning at the top of the screen naming various Montana counties as targets for the spoof announcement of doom, which sparked calls to the state's cops.

As could be expected, KRTC promptly disavowed the bogus alert and the whole incident. The perpetrators behind this epic prank call still remain unknown to this day.

Initial investigations suggested that weak default passwords on emergency alert systems accessible over the internet may have been used to pull off the hack. But this still remains unconfirmed, even after five months.

But now researchers at IO-Active have found that systems used to receive and authenticate emergency alert messages are vulnerable to remote attack.

The security vulnerability is specific to Linux-powered application servers from two manufacturers, according to the US feds-- the Digital Alert Systems DASDEC-I and DASDEC-II servers, and the Monroe Electronics R-189 One-Net and R-189SE products, apparently all shipped with publicly downloadable firmware that contains private root SSH keys, a recent alert by the U.S. Cyber Emergency Response Team (CERT) warns.

“These DASDEC application servers are currently shipped with their root privileged SSH key as part of the firmware update package," explained Mike Davis, principal research scientist for IO-Active.

"This simple key allows an attacker to remotely log in over the internet and can manipulate any system function. For example, they could disrupt a station’s ability to transmit and could disseminate false emergency information. For any of these issues to be resolved, we believe that re-engineering needs to be done on the digital alerting system side and firmware updates to be pushed to all appliances.”

The EAS is designed to enable the President of the United States to speak to U.S. citizens within just ten minutes of a major disaster occurring.

In the past, such alerts were passed from station to station using the Associate Press (AP) or United Press International (UPI) “wire services” which connected to television and radio stations around the nation.

Whenever the station received an authenticated Emergency Action Notification (EAN), the station would disrupt its current broadcast to deliver the message to the public.

More recently, the system has been switched to a more automated and decentralised system. Once a station receives and authenticates the message, the DASDEC hardware interrupts transmission and overlays the message onto the broadcast with the alert tone containing information about the disaster.

The DASDEC application server receives and authenticates EAS messages so that security shortcomings with the technology are a serious concern.

IO-Active has also issued its own Labs advisory outlining the apparently affected products, the impact of such attacks and how to mitigate the issue.

According to CERT, a fixed version of the firmware is available that allows users to change their login keys, and should be applied to critical devices.

In other internet security news

On any given day, security flaws in server management technology create some hacking opportunities almost on par with direct physical access to servers, says Metasploit creator HD Moore.

The security problem arises from serious shortcomings involving baseboard management controllers, a type of embedded computer used to provide out-of-band monitoring for desktops and servers, which consists of technology installed on nearly all servers today.

To a lesser degree, the security issues also come the Intelligent Platform Management Interface (IPMI) protocol used by some system admins.

A potential hacker could be able to compromise a baseboard management controller (BMC), and should be able to compromise its parent server if he's knowledgeable.

Compromising a server would allow miscreants to copy data from any attached storage, make changes to the operating system, install a backdoor, capture credentials passing through the server, launch denial of service attacks, or simply wipe the hard drives clean, among many other things.

Attacks like that are easily possible according to Moore, Rapid7's chief research officer and creator of penetrating testing software Metasploit, because vulnerable services are accessible across the internet.

Various research by Moore discovered that around 308,000 IPMI-enabled BMCs were exposed on the web, and the list appears to be growing quite rapidly.

Approximately 195,000 of these devices only support IPMI 1.5, which doesn't provide any form of encryption. Another 113,000 of those devices support IPMI v2.0, which suffers from serious design flaws as well.

For instance, 53,000 IPMI v.2.0 systems are vulnerable to password bypass attacks because they rely upon a weak cipher suite. Passive scans by Moore separately discovered that about 35,000 Supermicro BMCs expose an exploitable Universal Plug and Play (UPnP) service.

The security shortcomings under discussion are well beyond the capability of script-kiddies and could only be abused by a very skilled and experienced hacker.

But even then, it would be wise for system admins and data center managers to listen to the warning in Moore's research.

A blog post by Moore provides recommendations on how enterprises and hosting providers can mitigate the security risk of having their servers hacked into.

A lot of this comes down to fairly basic elements-- firewalling vulnerable services, disabling the vulnerable Cipher 0 cryptosuite and using complex and secure passwords.

Supermicro system users should apply an updated firmware image as well. Previous research by Moore earlier this year revealed that everything from medical systems to traffic light boxes is wide open to hackers thanks to a lack of authentication checks.

If you need reliability when it comes to SMTP servers, get the best, get Port 587.

Get a powerful Linux Dual-Core dedicated server for less than $2.67 a day!

Share on Twitter.

Source: ReKey.

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