Security Recommendations to Prevent Cyber Intrusions

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US-CERT is providing this Technical Security Alert in response to recent, well-publicized intrusions into several government and private sector computer networks. Network administrators and technical managers should not only follow the recommended security controls information systems outlined in NIST 800-53 but also consider the following measures. These measures include both tactical and strategic mitigations and are intended to enhance existing security programs.


  • Deploy a Host Intrusion Detection System (HIDS) to help block and identify common attacks.
  • Use an application proxy in front of web servers to filter out malicious requests.
  • Ensure that the "allow URL_fopen" is disabled on the web server to help limit PHP vulnerabilities from remote file inclusion attacks.
  • Limit the use of dynamic SQL code by using prepared statements, queries with parameters, or stored procedures whenever possible. Information on SQL injections is available at
  • Follow the best practices for secure coding and input validation; use the secure coding guidelines available at: and
  • Review US-CERT documentation regarding distributed denial-of-service attacks: and
  • Disable active scripting support in email attachments unless required to perform daily duties.
  • Consider adding the following measures to your password and account protection plan.
    • Use a two factor authentication method for accessing privileged root level accounts.
    • Use minimum password length of 15 characters for administrator accounts.
    • Require the use of alphanumeric passwords and symbols.
    • Enable password history limits to prevent the reuse of previous passwords.
    • Prevent the use of personal information as password such as phone numbers and dates of birth.
    • Deploy NTLMv2 as the minimum authentication method and disable the use of LAN Managed passwords.
    • Use minimum password length of 8 characters for standard users.
    • Disable local machine credential caching if not required through the use of Group Policy Object (GPO). For more information on this topic see Microsoft Support articles 306992 and 555631.
    • Deploy a secure password storage policy that provides password encryption.
  • If an administrator account is compromised, change the password immediately to prevent continued exploitation. Changes to administrator account passwords should only be made from systems that are verified to be clean and free from malware.
  • Implement guidance and policy to restrict the use of personal equipment for processing or accessing official data or systems (e.g., working from home or using a personal device while at the office).
  • Develop policies to carefully limit the use of all removable media devices, except where there is a documented valid business case for its use. These business cases should be approved by the organization with guidelines for their use.
  • Implement guidance and policies to limit the use of social networking services at work, such as personal email, instant messaging, Facebook, Twitter, etc., except where there is a valid approved business case for its use.
  • Adhere to network security best practices. See for more information.
  • Implement recurrent training to educate users about the dangers involved in opening unsolicited emails and clicking on links or attachments from unknown sources. Refer to NIST SP 800-50 for additional guidance.
  • Require users to complete the agency's "acceptable use policy" training course (to include social engineering sites and non-work related uses) on a recurring basis.
  • Ensure that all systems have up-to-date patches from reliable sources. Remember to scan or hash validate for viruses or modifications as part of the update process.

The Microsoft Security Bulletin Summary for July 2011 describes multiple vulnerabilities in Microsoft Windows and Office. Microsoft has released updates to address the vulnerabilities.


A remote, unauthenticated attacker could execute arbitrary code, cause a denial of service, or gain unauthorized access to your files or system.


Apply updates

Microsoft has provided updates for these vulnerabilities in the Microsoft Security Bulletin Summary for July 2011. That bulletin describes any known issues related to the updates. Administrators are encouraged to note these issues and test for any potentially adverse effects. In addition, administrators should consider using an automated update distribution system such as Windows Server Update Services (WSUS).



July 19, 2011: Initial release|July 20, 2011: Updated|July 21, 2011: Updated|July 22, 2011: Updated

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