TREND MICRO THREAT ALERT: Backdoor Uses Evernote as “Command-and-Control Server”

Evernote is one of the more popular note-taking tools for its many users, primarily because of its functionality and ease of use, across platforms. Unfortunately, it may also provide the perfect cover for cybercriminals’ tracks.

Global cloud security leader Trend Micro, recently uncovered a malware that appears to be using Evernote as a communication and control (C&C) server. Detected as BKDR_VERNOT.A, the malware attempts to connect to Evernote via https://evernote.com/intl/zh-cn, which is a legitimate URL.

Figure 1. BKDR_VERNOT.A strings showing how it attempts to access Evernote

 Figure 2. BKDR_VERNOT.A connecting to Evernote

 Figure 3. BKDR_VERNOT.A logging into Evernote

The sample Trend Micro gathered consists of an executable file, which drops a .DLL file and injects it into a legitimate process. The said .DLL file performs the actual backdoor routines.

Once installed, BKDR_VERNOT.A can perform several backdoor commands such as downloading, executing, and renaming files. It then gathers information from the infected system, including details about its OS, timezone, user name, computer name, registered owner and organization.

But here’s the interesting part: BKDR_VERNOT.A retrieves its C&C server and queries its backdoor commands in the notes saved in its Evernote account. The backdoor may also use the Evernote account as a drop-off point for its stolen information.

However, during the testing, it was not able to login using the credentials embedded in the malware. This is possibly a security measure imposed by Evernote following its recent hacking issue.

As stealth is the name of the game, misusing legitimate services like Evernote is the perfect way to hide the bad guys’ tracks and prevent efforts done by the security researchers. Because BKDR_VERNOT.A generates legitimate network traffic, most antimalware products may not readily detect this behavior as malicious. This can be troubling news not only for ordinary Internet users, but also for organizations with employees using software like Evernote.

Though this is a clever maneuver to avoid detection, this is not the first time that a legitimate service like Evernote was used as a method of evasion. Late last year, BKDR_MAKADOCS.JG was found using Google Docs to communicate to its C&C server. Similarly, the file-hosting site Sendspace was used as a storage of stolen information by TSPY_SPCESEND.A, a spyware that gathers MS Word and Excel files. Malware like BKDR_MAKADOCS.JG, TSPY_SPCESEND and now BKDR_VERNOT.A only show the extent that online bad guys will go to to hide their schemes.

To avoid such threats, users must always be cautious with visiting unknown websites and opening email messages and enable a strong protection network, such as Trend Micro’s Smart Protection Network which detects both malware cited in this blog entry.