Original release date: August 28, 2015 | Last revised: August 30, 2015
US-CERT has observed an increase in Domain Name System (DNS) traffic from client systems within internal networks to publically hosted DNS servers. Direct client access to Internet DNS servers, rather than controlled access through enterprise DNS servers, can expose an organization to unnecessary security risks and system inefficiencies. This Alert provides recommendations for improving security related to outbound DNS queries and responses.
Client systems and applications may be configured to send DNS requests to servers other than authorized enterprise DNS caching name servers (also called resolving, forwarding or recursive name servers). This type of configuration poses a security risk and may introduce inefficiencies to an organization.
Unless managed by perimeter technical solutions, client systems and applications may connect to systems outside the enterprise’s administrative control for DNS resolution. Internal enterprise systems should only be permitted to initiate requests to and receive responses from approved enterprise DNS caching name servers. Permitting client systems and applications to connect directly to Internet DNS infrastructure introduces risks and inefficiencies to the organization, which include:
Bypassed enterprise monitoring and logging of DNS traffic; this type of monitoring is an important tool for detecting potential malicious network activity.
Bypassed enterprise DNS security filtering (sinkhole/redirect or blackhole/block) capabilities; this may allow clients to access malicious domains that would otherwise be blocked.
Client interaction with compromised or malicious DNS servers; this may cause inaccurate DNS responses for the domain requested (e.g., the client is sent to a phishing site or served malicious code).
Lost protections against DNS cache poisoning and denial-of-service attacks. The mitigating effects of a tiered or hierarchical (e.g., separate internal and external DNS servers, split DNS, etc.) DNS architecture used to prevent such attacks are lost.
Reduced Internet browsing speed since enterprise DNS caching would not be utilized.
Implement the recommendations below to provide a more secure and efficient DNS infrastructure. Please note that these recommendations focus on improving the security of outbound DNS query or responses and do not encompass all DNS security best practices.
Configure operating systems and applications (including lower-tier DNS servers intended to forward queries to controlled enterprise DNS servers) to use only authorized DNS servers within the enterprise for outbound DNS resolution.
Configure enterprise perimeter network devices to block all outbound User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) traffic to destination port 53, except from specific, authorized DNS servers (including both authoritative and caching/forwarding name servers).
Additionally, filtering inbound destination port 53 TCP and UDP traffic to only allow connections to authorized DNS servers (including both authoritative and caching/forwarding name servers) will provide additional protections.
Refer to Section 12 of the NIST Special Publication 800-81-2 for guidance when configuring enterprise recursive DNS resolvers. 
Microsoft Windows Systems, Adobe Flash Player, and Linux
Between June and July 2015, the United States Computer Emergency Readiness Team (US-CERT) received reports of multiple, ongoing and likely evolving, email-based phishing campaigns targeting U.S. Government agencies and private sector organizations. This alert provides general and phishing-specific mitigation strategies and countermeasures.
US-CERT is aware of three phishing campaigns targeting U.S. Government agencies and private organizations across multiple sectors. All three campaigns leveraged website links contained in emails; two sites exploited a recent Adobe Flash vulnerability (CVE-2015-5119) while the third involved the download of a compressed (i.e., ZIP) file containing a malicious executable file. Most of the websites involved are legitimate corporate or organizational sites that were compromised and are hosting malicious content.
Systems infected through targeted phishing campaigns act as an entry point for attackers to spread throughout an organization’s entire enterprise, steal sensitive business or personal information, or disrupt business operations.
Phishing Mitigation and Response Recommendations
Implement perimeter blocks for known threat indicators:
Email server or email security gateway filters for email indicators
Web proxy and firewall filters for websites or Internet Protocol (IP) addresses linked in the emails or used by related malware
DNS server blocks (blackhole) or redirects (sinkhole) for known related domains and hostnames
Remove malicious emails from targeted user mailboxes based on email indicators (e.g., using Microsoft ExMerge).
Identify recipients and possible infected systems:
Search email server logs for applicable sender, subject, attachments, etc. (to identify users that may have deleted the email and were not identified in purge of mailboxes)
Search applicable web proxy, DNS, firewall or IDS logs for activity the malicious link clicked.
Search applicable web proxy, DNS, firewall or IDS logs for activity to any associated command and control (C2) domains or IP addresses associated with the malware.
Review anti-virus (AV) logs for alerts associated with the malware. AV products should be configured to be in quarantine mode. It is important to note that the absence of AV alerts or a clean AV scan should not be taken as conclusive evidence a system is not infected.
Scan systems for host-level indicators of the related malware (e.g., YARA signatures)
For systems that may be infected:
Capture live memory of potentially infected systems for analysis
Take forensic images of potentially infected systems for analysis
Isolate systems to a virtual local area network (VLAN) segmented form the production agency network (e.g., an Internet-only segment)
Report incidents, with as much detail as possible, to the NCCIC.
Educate Your Users
Organizations should remind users that they play a critical role in protecting their organizations form cyber threats. Users should:
Exercise caution when opening email attachments, even if the attachment is expected and the sender appears to be known. Be particularly wary of compressed or ZIP file attachments.
Avoid clicking directly on website links in emails; attempts to verify web addresses independently (e.g., contact your organization’s helpdesk or sear the Internet for the main website of the organization or topic mentioned in the email).
Report any suspicious emails to the information technology (IT) helpdesk or security office immediately.
Basic Cyber Hygiene
Practicing basic cyber hygiene would address or mitigate the vast majority of security breaches handled by today’s security practitioners:
Privilege control (i.e., minimize administrative or superuser privileges)
Application whitelisting / software execution control (by file or location)
System application patching (e.g., operating system vulnerabilities, third-party vendor applications)
Security software updating (e.g., AV definitions, IDS/IPS signatures and filters)
Network segmentation (e.g., separate administrative networks from business-critical networks with physical controls and virtual local area networks)
For more information on cybersecurity best practices, users and administrators are encouraged to review US-CERT Security Tip: Handling Destructive Malware to evaluate their capabilities encompassing planning, preparation, detection, and response. Another resource is ICS-CERT Recommended Practice: Improving Industrial Control Systems Cybersecurity with Defense-In-Depth Strategies.
Original release date: July 14, 2015 | Last revised: July 15, 2015
Microsoft Windows systems with Adobe Flash Player installed.
Used in conjunction, recently disclosed vulnerabilities in Adobe Flash and Microsoft Windows may allow a remote attacker to execute arbitrary code with system privileges. Since attackers continue to target and find new vulnerabilities in popular, Internet-facing software, updating is not sufficient, and it is important to use exploit mitigation and other defensive techniques.
The following vulnerabilities illustrate the need for ongoing mitigation techniques and prioritization of updates for highly targeted software:
Adobe Flash use-after-free and memory corruption vulnerabilities (CVE-2015-5119, CVE-2015-5122, CVE-2015-5123) Adobe Flash Player contains critical vulnerabilities within the ActionScript 3 ByteArray, opaqueBackground and BitmapData classes. Exploitation of these vulnerabilities could allow a remote attacker to execute arbitrary code on a vulnerable system.
Microsoft Windows Adobe Type Manager privilege escalation vulnerability (CVE-2015-2387) The Adobe Type Manager module contains a memory corruption vulnerability, which can allow an attacker to obtain system privileges on an affected Windows system. The Adobe Type Manager is a Microsoft Windows component present in every version since NT 4.0. The primary impact of exploiting this vulnerability is local privilege escalation.
By convincing a user to visit a website or open a file containing specially crafted Flash content, an attacker could combine any one of the three Adobe Flash vulnerabilities with the Microsoft Windows vulnerability to take full control of an affected system.
A common attack vector for exploiting a Flash vulnerability is to entice a user to load Flash content in a web browser, and most web browsers have Flash installed and enabled. A second attack vector for Flash vulnerabilities is through a file (such as an email attachment) that embeds Flash content. Another technique leverages Object Linking and Embedding (OLE) capabilities in Microsoft Office documents to automatically download Flash content from a remote server.
An attacker who is able to execute arbitrary code through the Flash vulnerability could exploit the Adobe Type Manager vulnerability to gain elevated system privileges. The Adobe Type Manager vulnerability allows the attacker to bypass sandbox defenses (such as those found in Adobe Reader and Google Chrome) and low integrity protections (such as Protected Mode Internet Explorer and Protected View for Microsoft Office).
The Adobe Flash vulnerabilities can allow a remote attacker to execute arbitrary code. Exploitation of the Adobe Type Manager vulnerability could then allow the attacker to execute code with system privileges.
Since attackers regularly target widely deployed, Internet-accessible software such as Adobe Flash and Microsoft Windows, it is important to prioritize updates for these products to defend against known vulnerabilities.
Since attackers regularly discover new vulnerabilities for which updates do not exist, it is important to enable exploit mitigation and other defensive techniques.
The Microsoft Windows Adobe Type Manager vulnerability (CVE-2015-2387) is addressed in Microsoft security Bulletin MS15-077. Users are encouraged to review the Bulletin and apply the necessary updates.
Use the Microsoft Enhanced Mitigation Experience Toolkit (EMET)
EMET can be used to help prevent exploitation of the Flash vulnerabilities. In particular, Attack Surface Reduction (ASR) can be configured to help restrict Microsoft Office and Internet Explorer from loading the Flash ActiveX control. See the following link for additional information: http://www.microsoft.com/en-us/download/details.aspx?id=46366
Securing end-to-end communications plays an important role in protecting privacy and preventing some forms of man-in-the-middle (MITM) attacks. Recently, researchers described a MITM attack used to inject code, causing unsecured web browsers around the world to become unwitting participants in a distributed denial-of-service attack. That same code can be employed to deliver an exploit for a particular vulnerability or to take other arbitrary actions.
A MITM attack occurs when a third party inserts itself between the communications of a client and a server. MITM attacks as a general class are not new. Classic MITM attacks (e.g., ARP Spoofing) focus on redirecting network communications. By definition, network infrastructure under attacker control is vulnerable to MITM. However, as technology evolves, new methods for performing MITM attacks evolve as well.
Currently, there is no single technology or configuration to prevent all MITM attacks. However, increasing the complexity with multiple layers of defense may raise the cost for the attacker. Increasing the attacker’s cost in time, effort, or money can be an effective deterrent to avoiding future network compromise.
Generally, encryption and digital certificates provide an effective safeguard against MITM attacks, assuring both the confidentiality and integrity of communications. As a result, modern MITM attacks have focused on taking advantage of weaknesses in the cryptographic infrastructure (e.g., certificate authorities (CAs), web browser certificate stores) or the encryption algorithms and protocols themselves.
MITM attacks are critical because of the wide range of potential impacts—these include the exposure of sensitive information, modification of trusted data, and injection of data.
Employing multiple network and browser protection methods forces an attacker to develop different tactics, techniques, and procedures to circumvent the new security configuration.
US-CERT recommends reviewing the following mitigations to reduce vulnerability to MITM attacks:
Update Transport Layer Security and Secure Socket Layer (TLS/SSL)
US-CERT recommends upgrading TLS to 1.1 or higher and ensuring TLS 1.0 and SSL 1, 2, 3.x are disabled, unless required. TLS 1.0 clients can fall back to version 3.0 of the SSL protocol, which is vulnerable to a padding oracle attack when Cypher-Block Chaining mode is used. This method is commonly referred to as the "POODLE" (Padding Oracle on Downgraded Legacy Encryption) attack. Vulnerable TLS implementations can be updated by applying the patch provided by the vendor. Vendor information is available in the National Vulnerability Database (NVD) entry for CVE-2014-3566  or in CERT Vulnerability Note VU#577193 . See US-CERT TA14-290A  for additional information on this vulnerability.
Utilize Certificate Pinning
Certificate pinning  is a method of associating X.509 certificate and its public key to a specific CA or root. Typically, certificates are validated by checking a verifiable chain of trust back to a trusted root certificate. Certificate pinning bypasses this validation process and allows the user to trust “this certificate only” or “trust only certificates signed by this certificate.” Please use the following resources to configure your browser for certificate pinning:
Microsoft Certificate Trust
The Microsoft Enhanced Mitigation Experience Toolkit (EMET) 5.2 employs a feature named "Certificate Trust" for SSL/TLS certificate pinning. This feature is intended to detect and stop MITM attacks that leverage Public Key Infrastructure. 
To use the Certificate Trust, you must provide a list of websites you want to protect and certificate pinning rules applicable to those websites. In order to do this, work with the Certificate Trust Configuration feature of the graphical application or use the Configuration Wizard to automatically configure EMET with the recommended settings.  Also, ensure period defaults are updated through patching.
Browser Certificate Pinning
Google Chrome and Mozilla Firefox, among others, perform certificate pinning. They conduct a variation of certificate pinning using the HTTP Strict Transport Security (HSTS), which pre-loads a specific set of public key hashes into the HSTS configuration, limiting valid certificates to only those with the specified indicated public key. Chrome uses HTTPS pins for most Google properties. It uses whitelisted public keys which include keys from Verisign, Google Internet Authority, Equifax, and GeoTrust. Thus, Chrome will not accept certificates for Google properties from other CAs.
Firefox 32 on desktop and later (Firefox 34 and later on Android) has the ability to use certificate pinning. It also has the ability to enforce built-in pinsets (mapping of public keys) information to domains. Firefox will pin all sites that Chrome already does, pin their own sites after audit and cleansing, and pin other popular sites that are already in good standing. Please visit this site on How to Use Pinning  and for more information.
Implement DNS-based Authentication of Named Entities (DANE)
DANE is a protocol that allows certificates (X.509) commonly used for TLS. DANE is bound to DNS which uses Domain Name System Security Extensions (DNSSEC). A working group in the Internet Engineering Task Force of DANE developed a new type of DNS record that allows a domain itself to sign statements about which entities are authorized to represent it. 
Google Chrome does not use DANE but uses an add-on  for support. Mozilla Firefox also uses an add-on  to check the existence and validity of DNSSEC.
Use Network Notary Servers
Network notary servers aim to improve the security of communications between computers and websites by enabling browsers to verify website authenticity without relying on CAs. CAs are often considered a security risk because they can be compromised.  As a result, browsers can deem fraudulent sites trustworthy and are left vulnerable to MITM attacks.
Each network notary server, or group of servers, is public and can be operated by public/private organizations or individuals. These servers regularly monitor websites and build a history of each site’s certificate data over time. When a browser equipped with a network notary add-on communicates with a website and obtains its certificate information, a user-designated network notary server supplies the browser with historical certificate data for that site. If certificate information provided by the website is inconsistent with the notary’s historical data, a MITM attack could be at play. 
Original release date: April 29, 2015 | Last revised: May 06, 2015
Systems running unpatched software from Adobe, Microsoft, Oracle, or OpenSSL.
Cyber threat actors continue to exploit unpatched software to conduct attacks against critical infrastructure organizations. As many as 85 percent of targeted attacks are preventable .
This Alert provides information on the 30 most commonly exploited vulnerabilities used in these attacks, along with prevention and mitigation recommendations.
It is based on analysis completed by the Canadian Cyber Incident Response Centre (CCIRC) and was developed in collaboration with our partners from Canada, New Zealand, the United Kingdom, and the Australian Cyber Security Centre.
Unpatched vulnerabilities allow malicious actors entry points into a network. A set of vulnerabilities are consistently targeted in observed attacks.
A successful network intrusion can have severe impacts, particularly if the compromise becomes public and sensitive information is exposed. Possible impacts include:
Temporary or permanent loss of sensitive or proprietary information,
Disruption to regular operations,
Financial losses relating to restoring systems and files, and
Potential harm to an organization’s reputation.
Maintain up-to-date software
The attack vectors frequently used by malicious actors such as email attachments, compromised “watering hole” websites, and other tools often rely on taking advantage of unpatched vulnerabilities found in widely used software applications. Patching is the process of repairing vulnerabilities found in these software components.
It is necessary for all organizations to establish a strong ongoing patch management process to ensure the proper preventive measures are taken against potential threats. The longer a system remains unpatched, the longer it is vulnerable to being compromised. Once a patch has been publicly released, the underlying vulnerability can be reverse engineered by malicious actors in order to create an exploit. This process has been documented to take anywhere from 24-hours to four days. Timely patching is one of the lowest cost yet most effective steps an organization can take to minimize its exposure to the threats facing its network.
Patch commonly exploited vulnerabilities
Executives should ensure their organization’s information security professionals have patched the following software vulnerabilities. Please see patching information for version specifics.
Implement the following four mitigation strategies.
As part of a comprehensive security strategy, network administrators should implement the following four mitigation strategies, which can help prevent targeted cyber attacks.
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.
Patch applications such as Java, PDF viewers, Flash, web browsers and Microsoft Office.
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.
Patch operating system vulnerabilities.
Restrict administrative privileges to operating systems and applications based on user duties.
Restricting these privileges may prevent malware from running or limit its capability to spread through the network.
The Simda botnet – a network of computers infected with self-propagating malware – has compromised more than 770,000 computers worldwide .
The United States Department of Homeland Security (DHS), in collaboration with Interpol and the Federal Bureau of Investigation (FBI), has released this Technical Alert to provide further information about the Simda botnet, along with prevention and mitigation recommendations.
Since 2009, cyber criminals have been targeting computers with unpatched software and compromising them with Simda malware . This malware may re-route a user’s Internet traffic to websites under criminal control or can be used to install additional malware.
The malicious actors control the network of compromised systems (botnet) through backdoors, giving them remote access to carry out additional attacks or to “sell” control of the botnet to other criminals . The backdoors also morph their presence every few hours, allowing low anti-virus detection rates and the means for stealthy operation .
A system infected with Simda may allow cyber criminals to harvest user credentials, including banking information; install additional malware; or cause other malicious attacks. The breadth of infected systems allows Simda operators flexibility to load custom features tailored to individual targets.
Users are recommended to take the following actions to remediate Simda infections:
Keep your operating system and application software up-to-date - Install software patches so that attackers cannot take advantage of known problems or vulnerabilities. Many operating systems offer automatic updates. If this option is available, you should enable it (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 (examples below) that will help with the removal of Simda from your system.