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With its rich functionality and accessibility, Evernote is a popular note-taking tool for its many users. Unfortunately, it may also provide the perfect cover for cybercriminals’ tracks.

We 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 using https://evernote.com/intl/zh-cn as its referrer, perhaps to make it look like a malicious user.

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 we 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.

Unfortunately, during our 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 a 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 this threat, you must always be cautious with visiting unknown websites and opening email messages. Trend Micro Smart Protection Network detects both the malware cited in this blog entry.

Update as of April 4, 2013 1:00 AM PDT

We have been in communication with Evernote regarding this incident, and are working with them to detect any other malware that may attempt to use Evernote for malicious purposes.

We also wish to reiterate that BKDR_VERNOT.A was unable to actually log into Evernote because of the incorrect credentials that were hard-coded into the malware. No notes or other information on Evernote servers was actually read, created, or modified.

Had the malware been successful in accessing the notes, it would have used the Evernote account to:

• Retrieve information about C&C server in one of the notes saved
• Obtain backdoor commands from the notes saved
• Use the Evernote account as a drop-off point for stolen information

After getting commands from the Evernote account, the malware would have been able to execute the following backdoor commands:

• Download files
• Execute files
• Rename files
• Unzip archive files