1. Symantec/
  2. Security Response/
  3. Trojan.LowZones


Risk Level 1: Very Low

March 27, 2005
April 6, 2005 8:16:31 PM
Systems Affected:
Trojan.LowZones is a detection name used by Symantec to identify malicious software programs that share the primary functionality of lowering Internet Explorer security settings.

Background information
Since the late 1990s — when it became the Web browser with the largest market share — Internet Explorer has been a target for attackers. Designed with ease-of-use in mind, the browser sought to hide the complexities of browser security from the user. This meant that certain features that could be used by attackers to compromise security were enabled by default. Over the years, however, browser security has been improved, and the default Internet Explorer security settings now block or significantly restrict many avenues of attack. This means that attackers must first lower browser security settings in order to perform further malicious actions, and one way to achieve this objective is to create programs to do so. Symantec uses the detection name Trojan.LowZones for these such programs.

The Internet Explorer security model
Internet Explorer uses four 'zones' for security:
  • Internet
  • Local intranet
  • Trusted sites
  • Restricted sites

Each zone may be assigned a 'security level' from high to low, or alternatively the user may choose to customize the settings for each zone in more detail.

Programs detected as Trojan.LowZones typically perform one or more of the following actions:
  • Alter Internet zone settings to enable or unblock certain Web features and technologies
  • Add certain websites to the Trusted zone
  • Remove certain websites from the Restricted zone

The following sections detail ways in which attackers may alter security settings to achieve certain aims.

Trusted site settings
Programs detected as Trojan.LowZones may add certain websites to the Internet Explorer Trusted sites list, which allows them to perform potentially malicious actions. The websites may be the attacker's own, or alternatively may be run by affiliate groups.

User prompting settings
The Trojans may alter settings so that the user is not prompted when a file is downloaded. The user may then be coerced into clicking on a link to a malicious executable, which results in the file being downloaded on to the compromised computer.

Browser safety feature settings

Attackers may configure programs detected as Trojan.LowZones to disable certain safety features built in to the browser, which may include the following:
  • Pop-up blockers
  • Phishing filters
  • Scripting language restrictions
  • Signed code checks
  • User authentication mechanisms

With these features disabled, users will be vulnerable to the attack vectors that the safety features attempt to guard against.

Browser control settings
Most modern browsers by default do not allow websites to perform certain actions that may confuse, mislead, or annoy the user. Actions such as the creation of windows with no address or status bars may be unblocked by Trojan.LowZones.

Privacy setttings
Programs detected as Trojan.LowZones may alter security settings to allow JavaScript to access the clipboard, which may result in confidential information being made available to attackers.

ActiveX and .NET settings
An attacker may alter ActiveX and .NET settings so that they can load further malicious code on to the compromised computer. The attacker may also attempt to exploit known or unknown vulnerabilities in the browser or its associated plugins, which may lead to the execution of arbitrary code.

Changes to the registry
The Trojans lower security settings by creating and/or modifying registry entries under the following registry subkeys to alter the permissions of the websites in each security zone in Internet Explorer:
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Zones
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Lockdown_Zones
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Lockdown_Zones

Programs detected as Trojan.LowZones may also create and/or modify registry entries under the following registry subkeys to alter the websites that are in each zone:
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\Domains
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\Domains

Are there any tell-tale signs?
The following symptoms may be observed on a computer that has been compromised by Trojan.LowZones:
  • Internet Explorer runs slowly or crashes unexpectedly
  • The user is redirected to certain websites
  • Internet Explorer behavior changes without action from the user
  • Advertisements are displayed on the computer
  • The user is able to visit certain websites that previously were blocked, or unable to visit certain websites that previously could be visited

Trojan.LowZones is often the first step of a combined or multi-stage attack and as such the symptoms of other malware may be observed on the compromised computer.

What are the risks?
With the Web browser now used for online shopping, banking, social networking, and entertainment, it has become one of the most popular targets for attackers. Programs detected as Trojan.LowZones seek to compromise browser security, which means that Web browsing is no longer secure.

Lowered security settings mean that attackers may be able to download files and hoist further malware on to compromised computers. The malware may open a back door, steal information, attack other systems, or perform any other action.

What can I do to minimize the risks?
Users may choose to use an alternative browser to Internet Explorer, such as Mozilla Firefox, Google Chrome, or Opera.

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.

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.


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: Henry Bell
Summary| Technical Details| Removal

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