Month: February 2018

A serious vulnerability has been discovered in Microsoft-owned most popular free web messaging and voice calling service Skype that could potentially allow attackers to gain full control of the host machine by granting system-level privileges to a local, unprivileged user.

The worst part is that this vulnerability will not be patched by Microsoft anytime soon.

It’s not because the flaw is unpatchable, but because fixing the vulnerability requires a significant software rewrite, which indicates that the company will need to issue an all-new version of Skype rather than just a patch.

The vulnerability has been

discovered

and reported to Microsoft by security researcher Stefan Kanthak and resides in Skype’s update installer, which is susceptible to Dynamic Link Libraries (DLL) hijacking.

According to the researcher, a potential attacker could exploit the “functionality of the Windows DLL loader where the process loading the DLL searches for the DLL to be loaded first in the same directory in which the process binary resides and then in other directories.”

The exploitation of this preferential search order would allow the attacker to hijack the update process by downloading and placing a malicious version of a DLL file into a temporary folder of a Windows PC and renaming it to match a legitimate DLL that can be modified by an unprivileged user without having any special account privileges.

When Skype’s update installer tries to find the relevant DLL file, it will find the malicious DLL first, and thereby will install the malicious code.

Although Kanthak demonstrated the attack using the Windows version of Skype, he believes the same DLL hijacking method could also work against other operating systems, including Skype versions for macOS and Linux.

Kanthak informed Microsoft of the Skype vulnerability back in September, but the company told him that the patch would require the Skype update installer go through “a large code revision,” Kanthak

told

ZDNet.

So rather than releasing a security update, Microsoft decided to build an altogether new version of the Skype client that would address the vulnerability.

It should be noted that this vulnerability only affects the Skype for the desktop app, which uses its update installer which is vulnerable to the DLL hijacking technique. The Universal Windows Platform (UWP) app version available from the Microsoft Store for Windows 10 PCs is not affected.

The vulnerability has been rated as “medium” in severity, but Kanthak said, “the attack could be easily weaponized.” He gave two examples, which have not been released yet.

Until the company issues an all-new version of Skype client, users are advised to exercise caution and avoid clicking on attachments provided in an email. Also, make sure you run appropriate and updated anti-virus software that offers some defence against such attacks.

This is not the first time Skype has been dealing with a severe security flaw. In June 2017, a

critical flaw in Skype

was revealed before Microsoft released a fix for the issue that allowed hackers to crash systems and execute malicious code in them.

Last month, among several messaging applications, Skype was also dealing with a critical remote code execution

vulnerability in Electron

—a popular web application framework widely-used in desktop applications.

A zero-day vulnerability has been discovered in the desktop version for end-to-end encrypted Telegram messaging app that was being exploited in the wild in order to spread malware that mines cryptocurrencies such as Monero and ZCash.

The Telegram vulnerability was uncovered by security researcher Alexey Firsh from Kaspersky Lab last October and affects only the Windows client of Telegram messaging software.

The flaw has actively been exploited in the wild since at least March 2017 by attackers who tricked victims into downloading malicious software onto their PCs that used their CPU power to mine cryptocurrencies or serve as a backdoor for attackers to remotely control the affected machine, according to a

blogpost

on Securelist.

Here’s How Telegram Vulnerability Works

The vulnerability resides in the way Telegram Windows client handles the RLO (right-to-left override) Unicode character (U+202E), which is used for coding languages that are written from right to left, like Arabic or Hebrew.

According to Kaspersky Lab, the malware creators used a hidden RLO Unicode character in the file name that reversed the order of the characters, thus renaming the file itself, and send it to Telegram users.

For example, when an attacker sends a file named "photo_high_re*U+202E*gnp.js" in a message to a Telegram user, the file’s name rendered on the users’ screen flipping the last part.

Therefore, the Telegram user will see an incoming PNG image file (as shown in the below image) instead of a JavaScript file, misleading into downloading malicious files disguised as the image.

"As a result, users downloaded hidden malware which was then installed on their computers," Kaspersky says in its press release published today.

Kaspersky Lab reported the vulnerability to Telegram and the company has since patched the vulnerability in its products, as the Russian security firm said: "at the time of publication, the zero-day flaw has not since been observed in messenger’s products."

Hackers Used Telegram to Infect PCs with Cryptocurrency Miners

During the analysis, Kaspersky researchers found several scenarios of zero-day exploitation in the wild by threat actors. Primarily, the flaw was actively exploited to deliver cryptocurrency mining malware, which uses the victim’s PC computing power to mine different types of cryptocurrency including Monero, Zcash, Fantomcoin, and others.

While analyzing the servers of malicious actors, the researchers also found archives containing a Telegram’s local cache that had been stolen from victims.

In another case, cybercriminals successfully exploited the vulnerability to install a backdoor trojan that used the Telegram API as a command and control protocol, allowing hackers to gain remote access to the victim’s computer.

"After installation, it started to operate in a silent mode, which allowed the threat actor to remain unnoticed in the network and execute different commands including the further installation of spyware tools," the firm added.

Firsh believes the zero-day vulnerability was exploited only by Russian cybercriminals, as "all the exploitation cases that [the researchers] detected occurring in Russia," and a lot of artifacts pointed towards Russian cybercriminals.

The best way to protect yourself from such attacks is not to download or open files from unknown or untrusted sources.

The security firm also recommended users to avoid sharing any sensitive personal information in messaging apps and make sure to have a good antivirus software from reliable company installed on your systems.

A zero-day vulnerability has been discovered in the desktop version for end-to-end encrypted Telegram messaging app that was being exploited in the wild in order to spread malware that mines cryptocurrencies such as Monero and ZCash.

The Telegram vulnerability was uncovered by security researcher Alexey Firsh from Kaspersky Lab last October and affects only the Windows client of Telegram messaging software.

The flaw has actively been exploited in the wild since at least March 2017 by attackers who tricked victims into downloading malicious software onto their PCs that used their CPU power to mine cryptocurrencies or serve as a backdoor for attackers to remotely control the affected machine, according to a

blogpost

on Securelist.

Here’s How Telegram Vulnerability Works

The vulnerability resides in the way Telegram Windows client handles the RLO (right-to-left override) Unicode character (U+202E), which is used for coding languages that are written from right to left, like Arabic or Hebrew.

According to Kaspersky Lab, the malware creators used a hidden RLO Unicode character in the file name that reversed the order of the characters, thus renaming the file itself, and send it to Telegram users.

For example, when an attacker sends a file named "photo_high_re*U+202E*gnp.js" in a message to a Telegram user, the file’s name rendered on the users’ screen flipping the last part.

Therefore, the Telegram user will see an incoming PNG image file (as shown in the below image) instead of a JavaScript file, misleading into downloading malicious files disguised as the image.

"As a result, users downloaded hidden malware which was then installed on their computers," Kaspersky says in its press release published today.

Kaspersky Lab reported the vulnerability to Telegram and the company has since patched the vulnerability in its products, as the Russian security firm said: "at the time of publication, the zero-day flaw has not since been observed in messenger’s products."

Hackers Used Telegram to Infect PCs with Cryptocurrency Miners

During the analysis, Kaspersky researchers found several scenarios of zero-day exploitation in the wild by threat actors. Primarily, the flaw was actively exploited to deliver cryptocurrency mining malware, which uses the victim’s PC computing power to mine different types of cryptocurrency including Monero, Zcash, Fantomcoin, and others.

While analyzing the servers of malicious actors, the researchers also found archives containing a Telegram’s local cache that had been stolen from victims.

In another case, cybercriminals successfully exploited the vulnerability to install a backdoor trojan that used the Telegram API as a command and control protocol, allowing hackers to gain remote access to the victim’s computer.

"After installation, it started to operate in a silent mode, which allowed the threat actor to remain unnoticed in the network and execute different commands including the further installation of spyware tools," the firm added.

Firsh believes the zero-day vulnerability was exploited only by Russian cybercriminals, as "all the exploitation cases that [the researchers] detected occurring in Russia," and a lot of artifacts pointed towards Russian cybercriminals.

The best way to protect yourself from such attacks is not to download or open files from unknown or untrusted sources.

The security firm also recommended users to avoid sharing any sensitive personal information in messaging apps and make sure to have a good antivirus software from reliable company installed on your systems.