Tag Archives: US-CERT

Is Your Organization Prepared? New Details on HIDDEN COBRA Botnet

North Korea’s HIDDEN COBRA botnet is targeting organizations in the finance sector, media, aerospace, and critical infrastructure around the globe with disruptive DDoS attacks.

The team at US-CERT issued an alert including technical details on the tools and infrastructure used by the botnet: DDoS, keyloggers, remote access tools, and wiper malware.

The alert notes common vulnerabilities used by these cyber criminals:

  • CVE-2015-6585: Hangul Word Processor Vulnerability
  • CVE-2015-8651: Adobe Flash Player and 19.x Vulnerability
  • CVE-2016-0034: Microsoft Silverlight 5.1.41212.0 Vulnerability
  • CVE-2016-1019: Adobe Flash Player Vulnerability
  • CVE-2016-4117: Adobe Flash Player Vulnerability

Organizations should update these applications as soon as possible to reflect the latest version and patches. Better yet, if you don’t need Adobe Flash or Microsoft Silverlight, remove them from your system altogether.

Indicators of compromise are included in the alert. Network administrators should review the IP addresses, file hashes, network signatures, and YARA rules provided. Additionally, add the IP addresses associated with HIDDEN COBRA to the watchlist to observe any potential malicious activity.

Key Takeaway

Unpatched applications continue to be a weak point for organizations. Vulnerabilities in Flash and Silverlight are commonly targeted by HIDDEN COBRA to spread malware. The US-CERT alert gives network administrators a good jump start on protecting their systems from the active botnet. Now the onus is on organizations to implement the information.

HIDDEN COBRA: North Korean Malicious Cyber Activity

The Department of Homeland Security (DHS) and the Federal Bureau of Investigation (FBI) have published a joint technical alert that identifies Internet Protocol (IP) addresses that appear to host resources infected with a malware variant used to manage North Korea’s distributed denial of service botnet infrastructure. The intent of sharing this information is to enable network defenders to identify and reduce exposure to North Korean government cyber activity.

The technical alert can be accessed here.

Threat Alert: Patch Critical for Samba Vulnerability

All versions of Samba from 3.5.0 onwards are susceptible to a remote code execution vulnerability, allowing a malicious client to upload a shared library to a writable share, and then cause the server to load and execute it. This advisory warning was released by Samba maintainers on Wednesday, urging Samba vendors and administrators of the networking utility to install a patch on any affected version as soon as possible.

Samba provides file and print services for clients using the SMB protocol (yes, same protocol leveraged in the WannaCry attacks) including Windows and Linux.

The vulnerability – CVE-2017-7494 – could give an attacker the ability to execute arbitrary code on a device with root-level privileges.

Samba notes this might disable some expected functionality for Windows clients. Additionally, older devices may not be receiving a patch for the firmware or operating system. If workarounds are not possible, devices should be considered insecure.

Given the ease and reliability of exploits, as we have seen with WannaCry attacks, this hole is worth plugging as soon as possible. It’s only a matter of time until attackers begin actively targeting this vulnerability.

How are WannaCry, EternalRocks (WannaCry 2.0) and this Samba alert related?

Windows has had a vulnerability in Server Messaging Block (SMB or Samba), which is an integral service related to network file sharing, since 2008. The NSA developed a tool to exploit this vulnerability called ETERNALBLUE. ETERNALBLUE is the attack agent used to spread WannaCry/EternalRocks.

When the exploit was released to the public by the ShadowBrokers crew a month ago, Microsoft acted very quickly and released the MS17-010 patch to address it. Those who have MS17-010 installed are, and continue to be safe from the issue.

This US-CERT alert is for the Linux/UNIX version of Samba. It’s evident that the maintainers of this codebase took lessons learned from WannaCry and realized that their version of SMB service is susceptible to a similar but not equivalent problem.

Be Aware of Hurricane Matthew Phishing Scams

us-cert-logo[This is a recent threat alert from US-CERT. Please share with others in your organization and make sure employees are aware of the threats and consequences of these phishing scams and emails.]

US-CERT warns users to remain vigilant for malicious cyber activity seeking to capitalize on interest in Hurricane Matthew. Users are advised to exercise caution in handling any email with subject line, attachments, or hyperlinks related to Hurricane Matthew, even if it appears to originate from a trusted source. Fraudulent emails will often contain links or attachments that direct users to phishing or malware-infected websites. Emails requesting donations from deceptive charitable organizations commonly appear after major natural disasters.

US-CERT encourages users and administrators to use caution when encountering these types of email messages and take the following preventative measures to protect themselves from phishing scams and malware campaigns:

  • Do not follow unsolicited web links in email messages.
  • Use caution when opening email attachments. Refer to the Using Caution with Email Attachments Cyber Security Tip for more information on safely handling email attachments.
  • Keep antivirus and other computer software up-to-date.
  • Refer to the Avoiding Social Engineering and Phishing Attacks Cyber Security Tip for more information on social engineering attacks.
  • Review the Federal Trade Commission information on Charity Scams.
  • Verify the legitimacy of any email solicitation by contacting the organization directly through a trusted contact number. You can find trusted contact information for many charities on the BBB National Charity Report Index.

Phishing Alert: Earthquake Disaster Email Scams

US-CERT and the FTC have both issued alerts on email scams that cite the recent earthquakes in Ecuador and Japan. The scam emails may contain links or attachments that direct users to phishing or malware-infected websites. Donation requests from fraudulent charitable organizations commonly appear after major natural disasters.

Take the following measures to protect yourself from these scams:

  • Review the FTC alert and their information on Charity Scams.
  • Do not follow unsolicited web links or attachments in email messages.
  • Keep antivirus and other computer software up-to-date.
  • Check this Better Business Bureau (BBB) list for Ecuador Earthquake Relief before making any donations to this cause.

Threat Alert: Dorkbot

[US-CERT released this Threat Alert warning about Dorkbot.]

Systems Affected

Microsoft Windows


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.


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 an 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).


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.


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 Autorun­Dorkbot 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.


http://www.microsoft.com/security/scanner/en-us/default.aspx (link is external)

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


Security Alert: Web Shells

[US-CERT released this threat alert warning about web shells.]


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.

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.


Web shells such as China Chopper, WSO, C99 and B374K are frequently chosen by adversaries:

  • 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.

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.


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

Threat Alert: Dridex P2P Malware

[US-CERT released this threat alert warning about the Dridex malware.]

Dridex, a peer-to-peer (P2P) bank credential-stealing malware, uses a decentralized network infrastructure of compromised personal computers and web servers to execute command-and-control (C2).

Dridex is a multifunctional malware package that leverages obfuscated macros in Microsoft Office and extensible markup language (XML) files to infect systems. The primary goal of Dridex is to infect computers, steal credentials, and obtain money from victims’ bank accounts.

Operating primarily as a banking Trojan, Dridex is generally distributed through phishing email messages. The emails appear legitimate and are carefully crafted to entice the victim to click on a hyperlink or to open a malicious attached file. Once a computer has been infected, Dridex is capable of stealing user credentials through the use of surreptitious keystroke logging and web injects.

A system infected with Dridex may be employed to send spam, participate in distributed denial-of-service (DDoS) attacks, and harvest users’ credentials for online services, including banking services.

Best Practices

Users are recommended to take the following actions to remediate Dridex infections:

  • Use and maintain anti-virus software – Anti-virus software recognizes and protects your computer against most known viruses. Even though Dridex 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 (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 can’t take advantage of known problems or vulnerabilities. Many operating systems offer automatic updates. You should enable automatic updates if this option is available (see Understanding Patchesfor 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 (examples below) to help remove Dridex from your system.

Security Alert: PlugX Malware

A specific remote access malware – PlugX – that is being utilized in recent intrusions is reported to contain infrastructure originating from China. The PlugX malware has been used to compromise various U.S. Government and commercial industries including aerospace, entertainment, healthcare, and telecommunications networks. These intrusions resulted in the theft of sensitive information including bulk amounts of personally identifiable information.

The PlugX malware is delivered via spear phishing emails containing a malicious RTF or Word document which leverages exploit code for the CVE-2012-0158 vulnerability – including the Korplug, Gulpix, Kaba, Sogu and P2P variants. These malware types allow the following functions and operations on the infected host:

  • Collect running process and module information
  • Start/stop, load, and reconfigure system services
  • Create/delete files
  • Modify the system’s registry
  • Acquire detailed system information
  • Log user’s keystrokes
  • Capture screenshots
  • Monitor network resources and connections
  • Connect and make queries to SQL databases
  • Peer-to-Peer communication

Per US-CERT, the following top 5 practices are applicable to helping mitigate the impact of advanced adversaries using PlugX malware:

  • Application Whitelisting which limits the ability of malicious software and unapproved programs from running
  • Patch Applications (e.g., Java, PDF viewers, Flash, web browsers, and Microsoft Office)
  • Patch Operating System Vulnerabilities (used for extreme risk vulnerabilities)
  • Limit Administrative Privileges based on user position
  • Network Segmentation and Segregation into Security Zones – help protect sensitive information and critical services