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Trojan.Maliframe!html

Risk Level 1: Very Low

Discovered:
July 10, 2007
Updated:
July 10, 2007 11:40:58 AM
Type:
Trojan
Infection Length:
65 bytes; 67 bytes
Systems Affected:
Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows XP
Background details
The iframe element is not an inherently malicious HTML element. In fact, it has many positive uses. However, over the last number of years, attackers have discovered it is an easy way to carry off malicious code attacks like drive-by downloads. These malicious iframe elements are hosted on malicious websites, or in some cases, legitimate websites that have been hacked and had the iframe element inserted into their Web pages.

While an attack mechanism commonly found in drive-by downloading websites, the use of the iframe element is not limited to Web pages. It could also appear in emails, documents, or any sort of file type that supports HTML.


What is an iframe element?
The iframe element allows Web developers to include HTML content from other sources in their pages. A typical iframe element might look like this:

<iframe name="example" src=" http://www.example.com/example.html" width="640" height="280"></iframe>

A common real-world example that uses iframe elements are online banner ads. An advertiser creates the content in an HTML file that is hosted on a 3rd party website. A Web developer can then call this content within their own pages by adding the URL in an iframe element. The banner add then appears within the Web page they have created.


How are iframes used maliciously?

One of the features of the iframe element is width and height attributes. In most legitimate cases, such as the banner ad example above, a Web developer would specify the pixel size they would like the ad to appear.

However, a malicious attacker often sets these width and height attributes to zero pixels each. As a result, the iframe is invisible in a standard Web page, making it undetectable to the casual user. Such an iframe element might look like this if viewed in the markup:

<iframe name="malicious" src="http://www.example.com/malicious.html" width="0" height="0"></iframe>

The attacker then includes a malicious URL within the element. When a page that contains such an iframe element is visited, the malicious actions are carried out, without any sort of interaction by the visitor.


What sorts of activities can be carried out with a malicious iframe?
This largely depends on the code on the page the user is directed to through the iframe element. Almost anything that can be carried out on a Web page could be performed through an iframe, though one of the more popular malicious activities is using iframe elements in conjunction with exploit packs.

An exploit pack is a malicious program comprised of a group of exploits for known vulnerabilities. There are a wide variety of exploit packs out there, such as Mpack, Neosploit, Fragus, etc. These programs are often stored on a malicious server. When a user visits such a server, the exploit pack attempts to carry out a series of attacks against either the user’s browser or operating system.

If the exploit pack is successful in finding a vulnerability and then compromising the computer, the next stage of the attack can then proceed. This usually entails the downloading of additional malware files onto the compromised computer. In many cases this entails downloaders, infostealers, or back doors.

Iframe elements and exploit packs can also be used as a method of propagation when a Web server is compromised. After a successful attack in these cases, the threat dropped on the compromised computer may scan for Web files, such as .html, .asp, or .php files, adding a malicious iframe element to any that are found. Alternatively, attackers may use a SQL injection attack routine that adds an iframe into the fields of database tables, and thus any subsequent pages generated from the database.


What are the risks?
An iframe attack, the resulting exploit attempts, and the chances that further malicious code will be downloaded poses a relatively high risk of damaging a compromised computer. The risks vary, and depend on the success of the attack, but range from becoming part of a botnet, to loss of data, and even the chance of identity theft.


What can I do to minimize the risks?
As a general rule, users should always run up-to-date antivirus software with real-time protection such as Norton Antivirus, Norton Internet Security, Norton 360 or Symantec Endpoint Protection. In addition, a firewall -- or better still, an Intrusion Prevention System (IPS) -- will help to block back channel activities initiated by these types of malicious programs. Program controls such as those found in Symantec Endpoint Protection can also help to prevent unknown programs such as these from executing in the first place.

In order to prevent the exploit packs from successfully compromising a computer, it is also a good idea to ensure that all relevant security patches are installed.


How can I find out more?
Advanced users can submit a sample to Threat Expert to obtain a detailed report of the system and file system changes caused by a threat.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Ben Nahorney
Summary| Technical Details| Removal

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