Tag Archives: Security

TA16-105A: Apple Ends Support for QuickTime for Windows; New Vulnerabilities Announced

This post was originally published on this site

Original release date: April 14, 2016 | Last revised: September 29, 2016

Systems Affected

Microsoft Windows with Apple QuickTime installed

Overview

According to Trend Micro, Apple will no longer be providing security updates for QuickTime for Windows, leaving this software vulnerable to exploitation. [1]

Description

All software products have a lifecycle. Apple will no longer be providing security updates for QuickTime for Windows. [1]

The Zero Day Initiative has issued advisories for two vulnerabilities found in QuickTime for Windows. [2] [3]

Impact

Computer systems running unsupported software are exposed to elevated cybersecurity dangers, such as increased risks of malicious attacks or electronic data loss. Exploitation of QuickTime for Windows vulnerabilities could allow remote attackers to take control of affected systems.

Solution

Computers running QuickTime for Windows will continue to work after support ends. However, using unsupported software may increase the risks from viruses and other security threats. Potential negative consequences include loss of confidentiality, integrity, or availability of data, as well as damage to system resources or business assets. The only mitigation available is to uninstall QuickTime for Windows. Users can find instructions for uninstalling QuickTime for Windows on the Apple Uninstall QuickTime page. [4]

References

Revision History

  • April 14, 2016: Initial Release

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TA16-091A: Ransomware and Recent Variants

This post was originally published on this site

Original release date: March 31, 2016 | Last revised: September 29, 2016

Systems Affected

Networked Systems

Overview

In early 2016, destructive ransomware variants such as Locky and Samas were observed infecting computers belonging to individuals and businesses, which included healthcare facilities and hospitals worldwide. Ransomware is a type of malicious software that infects a computer and restricts users’ access to it until a ransom is paid to unlock it.

The United States Department of Homeland Security (DHS), in collaboration with Canadian Cyber Incident Response Centre (CCIRC), is releasing this Alert to provide further information on ransomware, specifically its main characteristics, its prevalence, variants that may be proliferating, and how users can prevent and mitigate against ransomware.

Description

WHAT IS RANSOMWARE?

Ransomware is a type of malware that infects computer systems, restricting users’ access to the infected systems. Ransomware variants have been observed for several years and often attempt to extort money from victims by displaying an on-screen alert. Typically, these alerts state that the user’s systems have been locked or that the user’s files have been encrypted. Users are told that unless a ransom is paid, access will not be restored. The ransom demanded from individuals varies greatly but is frequently $200–$400 dollars and must be paid in virtual currency, such as Bitcoin.

Ransomware is often spread through phishing emails that contain malicious attachments or through drive-by downloading. Drive-by downloading occurs when a user unknowingly visits an infected website and then malware is downloaded and installed without the user’s knowledge.

Crypto ransomware, a malware variant that encrypts files, is spread through similar methods and has also been spread through social media, such as Web-based instant messaging applications. Additionally, newer methods of ransomware infection have been observed. For example, vulnerable Web servers have been exploited as an entry point to gain access into an organization’s network.

WHY IS IT SO EFFECTIVE?

The authors of ransomware instill fear and panic into their victims, causing them to click on a link or pay a ransom, and users systems can become infected with additional malware. Ransomware displays intimidating messages similar to those below:

  • “Your computer has been infected with a virus. Click here to resolve the issue.”
  • “Your computer was used to visit websites with illegal content. To unlock your computer, you must pay a $100 fine.”
  • “All files on your computer have been encrypted. You must pay this ransom within 72 hours to regain access to your data.”

PROLIFERATION OF VARIANTS

In 2012, Symantec, using data from a command and control (C2) server of 5,700 computers compromised in one day, estimated that approximately 2.9 percent of those compromised users paid the ransom. With an average ransom of $200, this meant malicious actors profited $33,600 per day, or $394,400 per month, from a single C2 server. These rough estimates demonstrate how profitable ransomware can be for malicious actors.

This financial success has likely led to a proliferation of ransomware variants. In 2013, more destructive and lucrative ransomware variants were introduced, including Xorist, CryptorBit, and CryptoLocker. Some variants encrypt not just the files on the infected device, but also the contents of shared or networked drives. These variants are considered destructive because they encrypt users’ and organizations’ files, and render them useless until criminals receive a ransom.

In early 2016, a destructive ransomware variant, Locky, was observed infecting computers belonging to healthcare facilities and hospitals in the United States, New Zealand, and Germany. It propagates through spam emails that include malicious Microsoft Office documents or compressed attachments (e.g., .rar, .zip). The malicious attachments contain macros or JavaScript files to download Ransomware-Locky files.

Samas, another variant of destructive ransomware, was used to compromise the networks of healthcare facilities in 2016. Unlike Locky, Samas propagates through vulnerable Web servers. After the Web server was compromised, uploaded Ransomware-Samas files were used to infect the organization’s networks.

LINKS TO OTHER TYPES OF MALWARE

Systems infected with ransomware are also often infected with other malware. In the case of CryptoLocker, a user typically becomes infected by opening a malicious attachment from an email. This malicious attachment contains Upatre, a downloader, which infects the user with GameOver Zeus. GameOver Zeus is a variant of the Zeus Trojan that steals banking information and is also used to steal other types of data. Once a system is infected with GameOver Zeus, Upatre will also download CryptoLocker. Finally, CryptoLocker encrypts files on the infected system, and requests that a ransom be paid.

The close ties between ransomware and other types of malware were demonstrated through the recent botnet disruption operation against GameOver Zeus, which also proved effective against CryptoLocker. In June 2014, an international law enforcement operation successfully weakened the infrastructure of both GameOver Zeus and CryptoLocker.

Impact

Ransomware not only targets home users; businesses can also become infected with ransomware, leading to negative consequences, including

  • temporary or permanent loss of sensitive or proprietary information,
  • disruption to regular operations,
  • financial losses incurred to restore systems and files, and
  • potential harm to an organization’s reputation.

Paying the ransom does not guarantee the encrypted files will be released; it only guarantees that the malicious actors receive the victim’s money, and in some cases, their banking information. In addition, decrypting files does not mean the malware infection itself has been removed.

Solution

Infections can be devastating to an individual or organization, and recovery can be a difficult process that may require the services of a reputable data recovery specialist.

US-CERT recommends that users and administrators take the following preventive measures to protect their computer networks from ransomware infection:

  • Employ a data backup and recovery plan for all critical information. Perform and test regular backups to limit the impact of data or system loss and to expedite the recovery process. Note that network-connected backups can also be affected by ransomware; critical backups should be isolated from the network for optimum protection.
  • Use application whitelisting to help prevent malicious software and unapproved programs from running. Application whitelisting is one of the best security strategies as it allows only specified programs to run, while blocking all others, including malicious software.
  • Keep your operating system and software up-to-date with the latest patches. Vulnerable applications and operating systems are the target of most attacks. Ensuring these are patched with the latest updates greatly reduces the number of exploitable entry points available to an attacker.
  • Maintain up-to-date anti-virus software, and scan all software downloaded from the internet prior to executing.
  • Restrict users’ ability (permissions) to install and run unwanted software applications, and apply the principle of “Least Privilege” to all systems and services. Restricting these privileges may prevent malware from running or limit its capability to spread through the network.
  • Avoid enabling macros from email attachments. If a user opens the attachment and enables macros, embedded code will execute the malware on the machine. For enterprises or organizations, it may be best to block email messages with attachments from suspicious sources. For information on safely handling email attachments, see Recognizing and Avoiding Email Scams. Follow safe practices when browsing the Web. See Good Security Habits and Safeguarding Your Data for additional details.
  • Do not follow unsolicited Web links in emails. Refer to the US-CERT Security Tip on Avoiding Social Engineering and Phishing Attacks or the Security Publication on Ransomware for more information.

Individuals or organizations are discouraged from paying the ransom, as this does not guarantee files will be released. Report instances of fraud to the FBI at the Internet Crime Complaint Center.

References

Revision History

  • March 31, 2016: Initial publication
  • May 6, 2016: Clarified guidance on offline backups
  • July 11, 2016: Added link to governmental interagency guidance on ransomware

This product is provided subject to this Notification and this Privacy & Use policy.

TA15-337A: Dorkbot

This post was originally published on this site

Original release date: December 03, 2015 | Last revised: September 29, 2016

Systems Affected

Microsoft Windows

Overview

Dorkbot is a botnet used to steal online payment, participate in distributed denial-of-service (DDoS) attacks, and deliver other types of malware to victims’ computers. According to Microsoft, the family of malware used in this botnet “has infected more than one million personal computers in over 190 countries over the course of the past year.” The United States Department of Homeland Security (DHS), in collaboration with the Federal Bureau of Investigation (FBI) and Microsoft, is releasing this Technical Alert to provide further information about Dorkbot.

Description

Dorkbot-infected systems are used by cyber criminals to steal sensitive information (such as user account credentials), launch denial-of-service (DoS) attacks, disable security protection, and distribute several malware variants to victims’ computers. Dorkbot is commonly spread via malicious links sent through social networks instant message programs or through infected USB devices.

In addition, Dorkbot’s backdoor functionality allows a remote attacker to exploit infected system. According to Microsoft’s analysis, a remote attacker may be able to:

  • Download and run a file from a specified URL;
  • Collect logon information and passwords through form grabbing, FTP, POP3, or Internet Explorer and Firefox cached login details; or
  • Block or redirect certain domains and websites (e.g., security sites).

Impact

A system infected with Dorkbot may be used to send spam, participate in DDoS attacks, or harvest users’ credentials for online services, including banking services.

Solution

Users are advised to take the following actions to remediate Dorkbot infections:

  • Use and maintain anti-virus software – Anti-virus software recognizes and protects your computer against most known viruses. Even though Dorkbot is designed to evade detection, security companies are continuously updating their software to counter these advanced threats. Therefore, it is important to keep your anti-virus software up-to-date. If you suspect you may be a victim of Dorkbot, update your anti-virus software definitions and run a full-system scan. (See Understanding Anti-Virus Software for more information.)
  • Change your passwords – Your original passwords may have been compromised during the infection, so you should change them. (See Choosing and Protecting Passwords for more information.)
  • Keep your operating system and application software up-to-date – Install software patches so that attackers cannot take advantage of known problems or vulnerabilities. You should enable automatic updates of the operating system if this option is available. (See Understanding Patches for more information.)
  • Use anti-malware tools – Using a legitimate program that identifies and removes malware can help eliminate an infection. Users can consider employing a remediation tool (see example below) to help remove Dorkbot from their systems.
  • Disable Autorun­ – Dorkbot tries to use the Windows Autorun function to propagate via removable drives (e.g., USB flash drive). You can disable Autorun to stop the threat from spreading.

Microsoft

https://www.microsoft.com/security/scanner/en-us/default.aspx

The above example does not constitute an exhaustive list. The U.S. Government does not endorse or support any particular product or vendor.

References

Revision History

  • December 3, 2015: Initial Publication

This product is provided subject to this Notification and this Privacy & Use policy.

TA15-314A: Compromised Web Servers and Web Shells – Threat Awareness and Guidance

This post was originally published on this site

Original release date: November 10, 2015 | Last revised: September 29, 2016

Systems Affected

Compromised web servers with malicious web shells installed

Overview

This alert describes the frequent use of web shells as an exploitation vector. Web shells can be used to obtain unauthorized access and can lead to wider network compromise. This alert outlines the threat and provides prevention, detection, and mitigation strategies.

Consistent use of web shells by Advanced Persistent Threat (APT) and criminal groups has led to significant cyber incidents.

This product was developed in collaboration with US-CERT partners in the United Kingdom, Australia, Canada, and New Zealand based on activity seen targeting organizations across these countries. The detection and mitigation measures outlined in this document represent the shared judgement of all participating agencies.

Description

Web Shell Description

A web shell is a script that can be uploaded to a web server to enable remote administration of the machine. Infected web servers can be either Internet-facing or internal to the network, where the web shell is used to pivot further to internal hosts.

A web shell can be written in any language that the target web server supports. The most commonly observed web shells are written in languages that are widely supported, such as PHP and ASP. Perl, Ruby, Python, and Unix shell scripts are also used.

Using network reconnaissance tools, an adversary can identify vulnerabilities that can be exploited and result in the installation of a web shell. For example, these vulnerabilities can exist in content management systems (CMS) or web server software.

Once successfully uploaded, an adversary can use the web shell to leverage other exploitation techniques to escalate privileges and to issue commands remotely. These commands are directly linked to the privilege and functionality available to the web server and may include the ability to add, delete, and execute files as well as the ability to run shell commands, further executables, or scripts.

How and why are they used by malicious adversaries?

Web shells are frequently used in compromises due to the combination of remote access and functionality. Even simple web shells can have a considerable impact and often maintain minimal presence.

Web shells are utilized for the following purposes:

  1. To harvest and exfiltrate sensitive data and credentials;
  2. To upload additional malware for the potential of creating, for example, a watering hole for infection and scanning of further victims;
  3. To use as a relay point to issue commands to hosts inside the network without direct Internet access;
  4. To use as command-and-control infrastructure, potentially in the form of a bot in a botnet or in support of compromises to additional external networks. This could occur if the adversary intends to maintain long-term persistence.

While a web shell itself would not normally be used for denial of service (DoS) attacks, it can act as a platform for uploading further tools, including DoS capability.

Examples

Web shells such as China Chopper, WSO, C99 and B374K are frequently chosen by adversaries; however these are just a small number of known used web shells. (Further information linking to IOCs and SNORT rules can be found in the Additional Resources section).

  • China Chopper A small web shell packed with features. Has several command and control features including a password brute force capability.
  • WSO Stands for “web shell by orb” and has the ability to masquerade as an error page containing a hidden login form.
  • C99 A version of the WSO shell with additional functionality. Can display the server’s security measures and contains a self-delete function.
  • B374K PHP based web shell with common functionality such as viewing processes and executing commands.

Delivery Tactics

Web shells can be delivered through a number of web application exploits or configuration weaknesses including:

  • Cross-Site Scripting;
  • SQL Injection;
  • Vulnerabilities in applications/services  (e.g., WordPress or other CMS applications);
  • File processing vulnerabilities (e.g., upload filtering or assigned permissions);
  • Remote File Include (RFI) and Local File Include (LFI) vulnerabilities;
  • Exposed Admin Interfaces (possible areas to find vulnerabilities mentioned above).

The above tactics can be and are combined regularly. For example, an exposed admin interface also requires a file upload option, or another exploit method mentioned above, to deliver successfully.

Impact

A successfully uploaded shell script may allow a remote attacker to bypass security restrictions and gain unauthorized system access.

Solution

Prevention and Mitigation

Installation of a web shell is commonly accomplished through web application vulnerabilities or configuration weaknesses. Therefore, identification and closure of these vulnerabilities is crucial to avoiding potential compromise. The following suggestions specify good security and web shell specific practices:

  • Employ regular updates to applications and the host operating system to ensure protection against known vulnerabilities.
  • Implement a least-privileges policy on the web server to:
    • Reduce adversaries’ ability to escalate privileges or pivot laterally to other hosts.
    • Control creation and execution of files in particular directories.
  • If not already present, consider deploying a demilitarized zone (DMZ) between your webfacing systems and the corporate network. Limiting the interaction and logging traffic between the two provides a method to identify possible malicious activity.
  • Ensure a secure configuration of web servers. All unnecessary services and ports should be disabled or blocked. All necessary services and ports should be restricted where feasible. This can include whitelisting or blocking external access to administration panels and not using default login credentials.
  • Utilize a reverse proxy or alternative service, such as mod_security, to restrict accessible URL paths to known legitimate ones.
  • Establish, and backup offline, a “known good” version of the relevant server and a regular change-management  policy to enable monitoring for changes to servable content with a file integrity system.
  • Employ user input validation to restrict local and remote file inclusion vulnerabilities.
  • Conduct regular system and application vulnerability scans to establish areas of risk. While this method does not protect against zero day attacks it will highlight possible areas of concern.
  • Deploy a web application firewall and conduct regular virus signature checks, application fuzzing, code reviews and server network analysis.

Detection

Due to the potential simplicity and ease of modification of web shells, they can be difficult to detect. For example, anti-virus products sometimes produce poor results in detecting web shells.

The following may be indicators that your system has been infected by a web shell. Note a number of these indicators are common to legitimate files. Any suspected malicious files should be considered in the context of other indicators and triaged to determine whether further inspection or validation is required.

  • Abnormal periods of high site usage (due to potential uploading and downloading activity);
  • Files with an unusual timestamp (e.g., more recent than the last update of the web applications installed);
  • Suspicious files in Internet-accessible locations (web root);
  • Files containing references to suspicious keywords such as cmd.exe or eval;
  • Unexpected connections in logs. For example:
    • A file type generating unexpected or anomalous network traffic (e.g., a JPG file making requests with POST parameters);
    • Suspicious logins originating from internal subnets to DMZ servers and vice versa.
  • Any evidence of suspicious shell commands, such as directory traversal, by the web server process. 

For investigating many types of shells, a search engine can be very helpful. Often, web shells will be used to spread malware onto a server and the search engines are able to see it. But many web shells check the User-Agent and will display differently for a search engine spider (a program that crawls through links on the Internet, grabbing content from sites and adding it to search engine indexes) than for a regular user. To find a shell, you may need to change your User-Agent to one of the search engine bots. Some browsers have plugins that allow you to easily switch a User-Agent. Once the shell is detected, simply delete the file from the server.

Client characteristics can also indicate possible web shell activity. For example, the malicious actor will often visit only the URI where the web shell script was created, but a standard user usually loads the webpage from a linked page/referrer or loads additional content/resources. Thus, performing frequency analysis on the web access logs could indicate the location of a web shell. Most legitimate URI visits will contain varying user-agents, whereas a web shell is generally only visited by the creator, resulting in limited user-agent variants.

References

Revision History

  • November 10, 2015: Initial Release
  • November 13, 2015: Changes to Title and Systems Affected sections

This product is provided subject to this Notification and this Privacy & Use policy.