Analysis: BugBear.E, aka BugBear.C, Tanatos.E and PWSteal Hooker Trojan, is a new variant of the BugBear worm discovered in the early morning hours of April 6, 2004. Updated anti-virus software did not detect BugBear.E at the time of its discovery.
BugBear.E uses a new Microsoft Corp.s Internet Explorer vulnerability to silently auto-execute itself on vulnerable computers. BugBear.E was authored with Microsoft Visual C++ and packed with UPX and uses the same keylogger DLL file used by BugBear.A. BugBear.E is about 52,736–52,772 bytes in size. The worms size varies and may exceed this sample range.
BugBear.E spreads via HTML e-mails with a ZIP archive containing a malicious HTM file. At least one sample has the e-mail attachment name of "Biology 121sUnit 4 Essays.zip," containing an HTM file with the same name but with an .htm extension instead.
If the malicious attachment is executed, the worm performs a mass-mailing and installs a keylogger onto the local computer to steal sensitive information. It attempts to create a copy of itself in the Windows System directory with a randomized filename and an .exe extension. DLL files are also created with randomized filenames, used to steal and store sensitive information in an encrypted form on the local computer.
To perform a mass mailing, BugBear harvests e-mail addresses from the local drive. The following file types are searched by the worm for e-mail addresses: DBX, EML, MBX, NCH, ODS, and TBB. It also scans a file called inbox, if found, for e-mails.
The worm collects a list of file names taken from files with extension .ini and .rdp on the local hard drive. The worm then randomly selects a file name from this list to create the attachment name. The attachment also arrives with a filename randomly chosen from the following list: "Card", "data", "Docs", "image", "images", "music", "news", "photo", "pics", "readme", "resume", "Setup", "song", and "video". The attachment may have one of the following extensions: EXE, HTM, PIF, SCR, or ZIP.
Once installed, BugBear.E is able to log keystrokes and steal sensitive information from the local computer. Specifically, the worm attempts to steal cookies, keylogging data, text from various windows, and clipboard data. The worm has a list of eight e-mail addresses and severs in the body of the worm. This data is used to send out malicious e-mails and data to the attacker.
Considerable precautions are warranted due to the success and payloads of former BugBear variants. The current prevalence of BugBear.E is difficult to gauge since it is very early in the outbreak and it is not detected by anti-virus software. Early data indicates that it is spreading in the wild to some degree, but the rate or degree of prevalence has not been firmly established at the time of writing this report. BugBear worms have traditionally had great success as a top ten worm for many months. As a result, this new variant of BugBear will likely have similar success.
Detection: Look for questionable files with a size of about 52k and ZIP attachments with an HTM file. Also look for a new EXE, DLL and other files created by the worm and the change to the Windows registry. The computer may also show degregaded performance once the mass mailings are initiated.
Workaround: User awareness is the best method of defense against this class of attack. Users must be wary of suspicious URLs and never follow links from untrusted sources.
Vendor Fix: Anti-virus vendors will likely release updated signature files to protect against this malicious code in the near future. Some anti-virus applications may detect this malicious code heuristically. Early reports indicate that the executable of BugBear.C is not detected by updated anti-virus software.
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