Banking Scam Revealed
by Secure Science Corporation
1 Overview Not all people that send undesirable email (spam) are the same. Their motives differ as greatly as their tools and technical abilities. This document uncovers a spam gang who seeks to acquire your banking information, and the response from one of the targeted victims: Citibank. This document describes the unique bulk-mailing tool used for recent rash of financial email scams. These scams target financial entities such as Citibank, Wells Fargo, Halifax Bank, eBay, and Yahoo. Only one specific spam gang uses this tool for these financial scams. This spam gang started slow with only a few members, but has increased in both gang membership and spam volume. All emails and headers are provided unmodified with the following exception: all personal information has been modified to protect the identity of the recipient. These modifications are denoted with bold and underlined typeset. Every effort has been made to retain the same data format without disclosing personal information. For data taken from the public domain, such as newsgroup postings and messages from open forums, no effort has been made to modify the data or protect the publicly disclosed recipient. 2 The Citibank Scam With the growth of online banking comes online fraud. These schemes vary from web sites that "look" like the actual financial institution to email asking for personal banking information. At first glance, the email below (Fig. 1) looks like just another one of these simple bank fraud schemes.
At a quick glance, this email appears to be from Citibank, as it contains a Citibank URL. But a closer inspection indicates a financial scam:
People who clicked on the link saw the Citibank web page and a popup that prompts for login information (Fig. 2, Fig. 3). Although the Citibank web page actually came from Citibank, the popup came from a non-Citibank server. Victims that entered banking information in the popup essentially gave their accounts to an unknown scam artist.
2.1 Mass Mailing Revisions The 29-Sep-2003 mass mailing (Fig. 1, Fig. 2, and Fig. 3) is actually the second revision of the fraudulent bank emails. The first revision appeared on 16-Aug-2003 and asked the recipient to view new banking terms and conditions. Users who clicked on the link were redirected to a server in China. The first revision included the recipient's email address as a field in the URL. The second revision replaced the address field with a series of random characters. The popup for the second revision only asked for the user's Card and PIN numbers. The third release on 25-Oct-2003 (Fig. 4) was revised to prompt for the user's Card number, PIN number, and expiration date. In nearly every case, a Russian server was used, either to host the requests, or to act as a web-bug and count the number of hits. For example, the web bug from the first revision can be found here. According to this web-log, there were 107,274 hits on 16-Aug-2003, and 91,573 hits on 17-Aug-2003 (Fig. 5). These were primarily due to responses to the first spam message. In contrast, the day before the mass mailing, there was only one web-log entry, from "68.82.62.191" - a cable modem in Tybouts Corner, Delaware. The Delaware system was used 8 out of 10 times in the week prior to the mass mailing [ref 3] (Fig. 6) and was likely used for testing the web server. It is unclear whether this is the IP address of the actual perpetrator or a compromised host. Network scans of the host suggest the presence of a firewall and no open proxy services, so it is unlikely that the host previously provided an open proxy [ref 4].
3 Linking Scams In order to operate a spam-based financial scam, three items are required: (1) a bulk mailing tool, (2) an individual or group to operate the tool, and (3) a method to collect victim information. By identifying these items, we can identify related scams by the same spam group, and distinguish these scams from scams initiated by other groups. 3.1 Bulk Mailing Tool People that send spam operate with millions of email addresses. To generate the emails within a reasonable amount of time, an automated email tool is used. Different tools have different unique traits. In the case of this Citibank scam, the tool has a unique "Message-ID" value in the email header: 16 to 17 characters consisting of "A-Z" and "0-9", followed by "@" and the forged sender's domain. Comparing this unique sequence to a large spam collection such as the Great Spam Archive [ref 5] (GSA) and the newsgroup news.admin.net-abuse.sightings (NANAS), we can identify similar messages. For example, between 11-Nov-1997 and 21-Aug-2003 the GSA recorded 17,867 spam messages. Of those, only 16 messages matched the unique signature of this specific bulk-mailing tool. All 16 matches were found clustered in the last five (5) months of the archive.
Although we expect the GSA to contain more entries by this bulk-mailing tool, the GSA is only updated periodically. The current archive ends on 21-Aug-2003, so more information will not be available until the GSA is updated. The narrow timeframe and near weekly appearance of spam from this bulk-mailing tool by the GSA recipient indicates a number of factors. First, there is likely only one or two senders using the tool; this tool does not have a large distribution. Second, the tool takes between 3 days and a week to cycle through the entire address list. Because the same email recipient does not receive every mass mailing, the spam gang is likely using subsets from their mailing list. The subsets may be due to a slow network connection (e.g., DSL or dialup) rather than an intentional selection of recipients. Finally, the minor change from 17 to 16 characters in the Message-ID, between the first and second observed messages, indicates that the sender is likely also the developer. 3.2 Scam Content Analysis Most of the email messages sent by this group contain grammatical errors and spelling errors (Fig. 7). For example, "I am the customer" is correct in Spanish, German, and other Slavic- and Latin-based languages, but proper English would be, "I am a customer." The errors are similar to those made by Europeans who have English as a second language. In addition, the currency notations match European notations ("300$" instead of "$300").
Although the spam topics used by this bulk-mailing tool rotate, there appears to be two distinct content types (Fig. 8, Fig. 9). The first type indicates a spam sender that delivers content for bulk-message customers (spammer for hire). The contents offer everything from discount software to penis enhancements. Other bulk-mailing tools have been observed delivering similar messages, but with western currency notations and common American grammatical errors. The grammatical errors and currency notations associated with this specific bulk-mailing tool suggests a European. The second content type is more interesting: many messages show a desire for banking and credit card information, or for users to download software. These messages do not have the same style of grammatical errors nor the European currency notation. This suggests a different sender than the bulk-message individual. This different sender is likely in the United States or Canada.
Besides the GSA, other spam archives have been analyzed. Some archives only contain the "bulk-messages" from this particular spam tool, other archives only contain the "financial fraud" messages, and many archives contain both types of messages. Based on the distinct differences in content, we can conclude that multiple groups use this specific bulk-mailing tool. However, the non-overlapping sending dates, independent mailing lists, and content text that is specific and unique to this tool indicates that (1) the group operating the financial fraud emails are different than the general bulk-message senders, and (2) the financial fraud emails are generated by a single spam gang. 3.3 Collecting Victim InformationThe financial fraud spam group appears to use multiple methods for gathering information from fraud victims. Initially the group requested responses by email. These emails went to unverified accounts that likely acted as blind-drops where the information would be either forwarded or gathered later.3.3.1 Use of MalwareFor a brief period, email messages sent by this particular financial fraud spam gang contained hostile attachments (malware). On 17-Jul-2003 a series of email messages were observed being sent from this particular bulk-mailing tool. The first content targeted E-Loan customers and included the "Trojan.Download.Berbew" [ref 6] malware. This trojan code was written in C (not C++ nor Java). This backdoor program attempts to steal passwords and send them to a remote web server. When used in conjunction with the bank scam, the system monitors passwords and presents the user with the actual bank login screen. Thus, when the user logs in, their bank account becomes compromised. On 22-Jul-2003, the same bulk-mailing tool generated a second wave of email. The second wave targeted Wells Fargo and Citibank customers, and included a newer version of Trojan.Download.Berbew.Trojan.Download.Berbew was not the only malware used by this group. On 26-Jul-2003, an email claiming to come from "admin@security.org" was observed. The text contents contained poor grammar and appeared to have been written in haste. The attachment contained the Exploit-Codebase [ref 7] malware. According to Network Associates:
Exploit-Codebase malware appears to have been written in C, similar to Trojan.Download.Berbew. While it is probable that the same individual created the Trojan.Download.Berbew and Exploit-Codebase malwares, it is unlikely that the malware author actually discovered the Expoit-Codebase vulnerability nearly a year prior. 3.3.2 Web ImpersonationsAfter using email blind-drops and malware, the group quickly progressed to impersonating web sites. The impersonation was done through web redirections. The hypertext transport protocol (HTTP) permits web servers to redirect requests to alternate sites (HTTP 303 return codes). In this case, the gang's web server returned an HTTP 303 return code redirecting browsers to the targeted financial institution. But, the HTTP response may also contain valid HTML code. The valid code usually tells the user that the page has been moved to a new location. This gang used the redirection response's HTML code to generate a popup requesting the victim's banking information. Thus, the main web page is the targeted financial institution, but the popup comes from a hostile server (Fig. 4). The hostile server acts as a blind-drop for victim information.3.4 Related Financial ScamsThe same bulk-mailing tool has been observed sending similar fraudulent content that targets many financial institutions. The table below presents dates and targets that are verifiable based on the sending email tool's unique fingerprint and common text within the messages. But, this is unlikely to be a complete list. Prior to July 2003, this spam gang appears to send "regular" bulk-mailing contents and not imitate financial login screens, a practice known as "phishing". In addition, there is no record of this particular spam tool being used by anyone prior to April 2003.Although this spam gang has targeted other financial groups, there is a strong emphasis on eBay and Citibank. This apparent preference may indicate a grudge, familiarity, specific knowledge, or specific access. The recent increase in banking targets may indicate a rush to capture more victims before being blacklisted, caught, or ignored. On 20-Oct-2003 the group attempted a 419 scam [ref 9]. Individuals rarely attempt the 419, or Nigerian scam, because this Ponzi scheme requires a noticeable amount of manpower and resources. The appearance of a 419 by this particular bulk-mailing tool indicates a likely increase in scam operators. There are many different groups that operate 419 scams; the text from this particular email was a poor copy of the 419 scam - other 419 gangs have better contents and better methods to identify themselves as the person in need. Due to the high volume of 419-style scams since April 2003, these approaches have become relatively common, easy to spot, and regularly ignored. In all likelihood, this financial fraud gang's attempt on 20-Oct-2003 was likely a failure. This may also account for the sudden increase in bank impersonations in the following days (5 banks targeted in 3 days). The group may have applied their additional manpower to their proven-successful strategy and simply branched out. In addition, the sudden focus change from USA financial sources to British banks (Barclays, Halifax, Nationwide, and Lloyds) at the end of October likely indicates new spam gang members with familiarity of the UK.
3.5 Unrelated Financial ScamsNot all financial fraud email messages can be attributed to this particular group. For example, this particular spam gang was not involved with requesting users to update eBay account information on 15-Oct-2003 and 17-Oct-2003; a different spam tool was used to distribute the fraudulent email messages. Additionally, the financial fraud messages from "verify@online-banking.net" that target financial institutions such as Citibank, Wells Fargo, Bank of America, Affinity Bank, and the Union Bank of California, all appear to be from a separate spam gang that focuses on banks located in California.4 Reporting to CitibankThe first financial-fraud email that we received (Fig. 1) claimed to be from Citibank. As such, we proceeded to report it to Citibank's online fraud reporting system (Fig. 10).
A few hours later, a response from Citibank was received (Fig. 11). Unfortunately, this reply has a significant number of questionable aspects. In particular:
No aspect of the email headers appears forged. The reply from Citibank originated from the Citibank Development Center in Los Angeles, California (CDCLA). It is now left to the reader to draw his own conclusions from this email.
5 Conclusion A single spam gang, using a unique bulk-mailing tool, appears responsible for the recent rash of financial fraud emails. This gang has targeted over a dozen financial sources, had dabbled in malware, and has struck over 20 times, showing what appears to be a serial pattern. Attempts to report these findings to Citibank were unsuccessful, and Citibank was unavailable for comment. Citibank has publicly stated that they do not know who has been victimized by the Citibank scams, nor do they know how many victims [ref 10]. In truth, their web logs very likely indicate exactly who fell victim to the 16-Aug-2003 fraudulent Citibank scheme. In addition, Citibank may not be able to identify "who" fell victim on 25-Sep-2003 and 25-Oct-2003 to the second and third revisions of the fraud scheme, but Citibank can identify "how many" victims are likely. This is because the fraudulent web sites used HTML links that directly referenced the financial institution's web site. 6 About the Author Secure Science Corporation is a professional services and software company that develops advanced technology dedicated to protecting online assets. Clients of Secure Science Corp. are provided with in-depth security evaluations, as well as cost-effective solutions, that are seamless in both deployment and maintenance. Secure Science Corp. is pioneering innovative ways to transform the Internet into a secure environment for both online communications and transactions. Comments on this article can be sent to e-response@securescience.net or to the SF editor. 7 Appendix A: Network Scans The initial fraudulent Citibank email that we received, leading toward this investigation, originated from "80.117.72.70". [Editor's note: this host is now down.] Network scans of host were conducted within five (5) minutes of receipt of the email. The scans indicate that the sending host was likely compromised. It is unclear whether the email sender was responsible for the compromise, or simply found a system with an open proxy server. 7.1 Italy DNS and Whois Scan Based on the IP address, we can identify the hosting company, country, and often the city. In addition, many service providers indicate the type of network connection. In this case, the host is located in Italy and provided by Telecom Italia. The host is on an ADSL connection.
7.2 Italy Nmap Results Nmap is a system utility for determining open services and operating system on a remote host. Nmap is available from http://www.insecure.org/nmap/.
7.3 Italy Nessus Results Nessus is a vulnerability scanner and can be used to determine if a host as unspecified services, or known system compromises. Nessus is available from http://www.nessus.org/.
8 Appendix B: GSA Email Message Summary The following table summarizes the email message from the Great Spam Archive that were sent by this group's unique bulk-mailing tool.
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References [1] The generic URL format is "http://[username[:password]@]server[:port]/path[?options]". Items in brackets ("[...]") are optional. In this email's URL, the string "www.citibank.com" is part of the username. The actual server is found after the "@" character. [2] Screen captures included without consent from SYNACK (no contact method available), <http://www.dslreports.com/forum/remark,8089564~root=scambusters~mode=flat>. [3] The Russian web-log can display the most used IP addresses. <http://www.hotlog.ru/cgi-bin/hotlog/site_stat/?id=126298&b_day=8&b_month=8&b_year=2003&e_day=15&e_month=8&e_ [4] Network scans of the Delaware host were performed periodically, between 26-Sep-2003 and 27-Oct-2003. Although the IP address may have been reassigned to a new host in the preceding month, DSL IP addresses are rarely rotated. The periodic scans have consistently provided the similar replies: no open ports, and many ports "filtered" or "closed". This suggests the same host with a firewall and no reassignment of the IP address. [5] The Great Spam Archive can be found at www.annexia.org. [6] Trojan.Download.Berbew is described at http://www.symantec.com/avcenter/venc/data/trojan.download.berbew.html and http://www.upenn.edu/computing/virus/03/trojan.download.berbew.html. [7] Exploit-Codebase is described at http://vil.nai.com/vil/content/v_99383.htm. [8] Source: http://vil.nai.com/vil/content/v_99383.htm. This quote has not been modified from the initial citation and is taken in context. [9] The "419 scam" is commonly known as the Nigerian scam and is a type of Ponzi scam. The name "419" comes from the relevant Nigerian criminal code. [10] Source: "Citibank warns customers of e-mail scam." Reuters. Aug. 18, 2003. http://news.com.com/2100-1017_3-5065394.html?tag=mainstry. [11] ibid, 6. [12] ibid, 7.
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