Phishing Technique One - Phishing Through Compromised Web Servers

Most phishing attacks that we have observed in the wild involve attackers breaking in to vulnerable servers and installing malicious web content. Honeynet technology allows us to capture in detail the typical life cycle of a phishing attack, and in general terms the flow of events we have observed during such incidents are as follows:

  • Attackers scan for vulnerable servers
  • Server is compromised and a rootkit or password protected backdoor installed
  • Phishers gain access to the server through this encrypted back door
  • If the compromised server is a web server, pre-built phishing web sites are downloaded
  • Some limited content configuration and web site testing is performed (potentially revealing the phisher's true IP address when they first access the web server)
  • Mass emailing tools are downloaded and used to advertise the fake web site via spam email
  • Web traffic begins to arrive at the phishing web site and potential victims access the malicious content

Often the time taken for this incident life cycle is only a matter of hours or days from when the system is first connected to the Internet, and our research suggests that such activity is taking place on many servers and targeting many organisations at once. We will illustrate these theories using data recorded during two incidents that are typical of common phishing attacks, using one incident observed by the German Honeynet Project and one incident observed by the UK Honeynet Project. In each case, vulnerable Linux honeypots were deployed by Honeynet Research Alliance members. The subsequent compromise of both honeypots shared a similar modus operandi: the vulnerable honeypots were scanned and compromised in quick succession, with pre-built phishing web sites and mass emailing tools for sending spam emails being uploaded and used by the attackers. Rootkits and IRC servers were also installed during these attacks, something we commonly observed in other similar incidents. The compromised honeypots were also used for several different purposes in addition to phishing: as an IRC bot by Romanian attackers and also as a scanner to locate and attack additional vulnerable computers (although the honeynet architecture prevented the attackers from successfully exploiting other servers from the compromised honeypots). Some interesting differences were also apparent, not least in the case of the UK incident, where several different groups accessed the compromised honeypot at the same time, making forensic analysis more complicated. For the sake of brevity, we have not included the details of these specific attacks in this paper and have only covered the lessons learned and how they apply to phishing. If you would like to review more details about the specific attacks, the following information is available:

The table below shows a summary of the key factors and differences between the incidents:

Data DE Incident UK Incident
Compromised honeypot Redhat Linux 7.1 x86. Redhat Linux 7.3 x86.
Location German corporate network. UK ISP data centre.
Attack method "Superwu" autorooter. "Mole" mass scanner.
Vulnerability exploited Wu-Ftpd File globbing heap corruption vulnerability (CVE-2001-0550). NETBIOS SMB trans2open buffer overflow (CAN-2003-0201).
Level of access gained Root. Root.
Rootkit installed Simple rootkit that backdoors several binaries. SHV4 rootkit.
Probable attackers Unknown. Multiple groups from cable modem IP ranges in Constanta region of Romania.
Web site activity Multiple pre-built phishing web sites downloaded targeting eBay and major US banks. Pre-built phishing web site downloaded targeting a major US bank.
Server side processing PHP script to validate user input. PHP script with more advanced user input validation and data categorisation.
Email activity Tried to send spam (example 1, example 2), but blocked by Honeywall. Only test emails sent, potentially to fellow phishers. Improved syntax and presentation.
Mass emailing method Basic PHP script from medium sized input list of email addresses. Basic PHP script from small input list of email addresses - possibly just a test.
Victim traffic reached honeypot No, spam advertisement and access to phishing web site blocked. Yes. 265 HTTP requests in 4 days, not due to spam sent from this server (no customer details were compromised).

From observing the phisher's keystrokes in both incidents (captured using Sebek), it is clear that the attackers connected to pre-existing back doors and immediately went to work deploying their phishing web sites. The attackers appeared to be familiar with the server environment, suggesting they were part of the group who originally compromised the honeypots, and that the phishing attempt was fairly well organised. As the uploaded web content often referred to other web servers and IP addresses, it is also likely that such activity was probably occurring on multiple servers at once.

Analysis of the phishing web site content downloaded by attackers during these incidents makes it clear that phishers are simultaneously targeting many well known online brands. Well constructed and officially branded pre-built fake web sites are routinely being deployed onto compromised servers - often targeting multiple organisations via separate "micro sites", with separate web server document roots, along with the necessary tools to propagate spam emails to potential phishing victims. Directory listings observed during FTP sessions also confirm that the attackers were heavily involved in spam and phishing activities, revealing pre-built web content and message delivery tools stored on a central server and appearing to target at least eBay, AOL, and several well known US banks in the case of the UK incident. These individual phishing attacks are unlikely to be isolated events, as the spam emails sent during the incidents often directed victims to a different web server than the compromised honeypot. This indicates that phishers are running multiple fake web servers and sending spam from multiple systems at once. Parallel phishing operations are also indicated by the timing of the first inbound HTTP request for phishing content after the UK honeypot was compromised:

2004-07-23 21:23:14.118902 XXX.XXX.XXX.XXX -> HTTP GET /.internetBankingLogon HTTP/1.1

This inbound HTTP request to the honeypot occurred before the attackers had finished setting up the fake online banking content on the honeypot, and confirms the hypothesis that the attacker knew in advance that this server was available for use as a phishing web site. Spam messages advertising the new phishing web site were already being emailed to victims from another host, even whilst the attacker was setting up the new phishing web site.

We were surprised by the number and range of source IP addresses making inbound HTTP requests to the compromised honeypot for the fake online banking content. The graph below shows the number of unique and repeat HTTP requests from individual IP addresses to the UK phishing web site before the honeypot was disconnected to protect end users (and the incident details logged with the targeted bank):

[image:images/HTTP%20access.JPG size=full]

A breakdown of the source top level DNS domains, countries and host operating systems accessing the phishing content on the UK honeypot can be found here. Note that before the honeypot was taken offline for forensic analysis, although web traffic for the phishing web site did arrive at the UK honeypot, no HTTP POST requests were made to the PHP script that processes users' data and therefore no user data was compromised during this phishing attack. In all the incidents discussed in this white paper, either the target organisation was notified of the incident and any relevant data was made available to them on request, or the local CERT was notified of any malicious activity. In all cases no compromised victim personal data was captured by Honeynet Project or Research Alliance members.

Data from these two example incidents suggests that phishers are active and organised, moving quickly between compromised computer systems and simultaneously targeting multiple well known brands. It also appears that a number of email users are regularly being tricked into accessing fake web interfaces for organisations such as online banks or retailers, and risk becoming victim's of phishing attacks.