United States: New Implementation Guidance For The US Cybersecurity Information Sharing Act

Signed into law on December 18, 2015, the Cybersecurity Information Sharing Act of 2015 (CISA) created new legal authorizations and protections for the sharing of cyber threat indicators and defensive measures between and within the private sector and the government (for more information, see our legal update, "Cybersecurity Information Sharing Act Signed Into US Law as Part of Omnibus Appropriations Legislation").1 CISA required various federal agencies to issue guidance, policies and procedures to support this information sharing. To that end, on February 16, 2016, the federal government released new implementation guidance to address:

  • Private entities' sharing of cyber threat indicators and defensive measures with the federal government;
  • Privacy and civil liberties procedures within the federal government;
  • Receipt of cyber threat indicators and defensive measures by the federal government; and
  • Sharing of cyber threat indicators by the federal government.2

In this update we discuss each of these four areas, with particular attention to provisions relevant to private entities.

"Guidance to Assist Non‐Federal Entities to Share Cyber Threat Indicators and Defensive Measures with Federal Entities under the Cybersecurity Information Sharing Act of 2015"

The "Non-Federal Entity Guidance" covers three topics: (i) key concepts, (ii) how to share cyber threat indicators and defensive measures with the federal government and (iii) protections for sharing entities.


Cyber Threat Indicator. The Non-Federal Entity Guidance summarizes CISA's authorization to share cyber threat indicators as permitting sharing only of "information that is directly related to and necessary to identify or describe a cybersecurity threat." The guidance expands on this summary by clarifying that "[i]nformation is not directly related to a cybersecurity threat if it is not necessary to assist others detect, prevent, or mitigate the cybersecurity threat." The guidance explains that, in the context of a spear phishing email, personal information about the sender of the email could be considered directly related to a cybersecurity threat, but personal information about the target typically would not meet that standard and, thus, should not be included as part of a cyber threat indicator.

It then adds "examples of information that would contain cyber threat indicators." These include:

  • A "technique that permits unauthorized access to an industrial control system,"
  • A "pattern of domain name lookups" corresponding to "malware infection,"
  • "[U]nexecuted malware found on [a] network," and
  • The "types of ... files that appear to have been exfiltrated" during a cyber attack.

The Non-Federal Entity Guidance observes that "[m]uch of the information within an indicator is centered on an observable fact about the cyber threat." This includes "internet protocol (IP) addresses," "file hashes" and "malware artifacts." The guidance explains that the "specificity and nature of the[se] observable facts are designed to reduce the risk that a cyber threat indicator contains personal content or information inappropriate to share."

Defensive Measures. The Non-Federal Entity Guidance notes that while defensive measures "will generally consist principally of technical information that can be used to detect and counter a cybersecurity threat," "personal information of a specific individual or that identifies a specific individual may occasionally be necessary to describe a cybersecurity threat." The guidance then provides a non-exhaustive list of examples of defensive measures, including:

  • A computer program that identifies malicious activity in web traffic flowing into an organization,
  • A signature that could be loaded into a company's intrusion detection system in order to detect a spear phishing campaign with particular characteristics, or
  • A firewall rule that disallows a type of malicious traffic from entering a network.

Information Protected Under Otherwise Applicable Privacy Laws. One of the stated goals of the Non-Federal Entity Guidance is "to help entities identify certain types of information protected under otherwise applicable privacy laws that are unlikely to be directly related to a cybersecurity threat." To that end, the guidance provides a nonexhaustive list of categories of protected information that likely will not qualify for sharing. These include: protected health information, human resource information, consumer information/history, education history, financial information, identifying information about property ownership and information protected under the Children's Online Privacy Protection Act.


The second section of the Non-Federal Entity Guidance provides direction on how a private entity should share cyber threat indicators and defensive measures with the federal government. It addresses requirements for sharing by non-federal entities and the means for such sharing. Before doing so, however, it emphasizes that "[s]haring conducted through the means discussed in this guidance that is conducted pursuant to CISA should not be construed to satisfy any statutory, regulatory, or contractual obligation" and that it "is intended to complement, not replace, the prompt reporting of any criminal activity, cyber incidents, or reportable events to the appropriate authorities."

Requirements for Non-Federal Entities. The Non-Federal Entity Guidance emphasizes the requirement imposed by CISA that a sharing non-federal entity review a cyber threat indicator for personal information prior to sharing. It "encourage[s]" non-federal entities to perform a "similar review prior to sharing defensive measures," and notes that "[a] defensive measure may contain a cyber threat indicator" that triggers the review requirement.

Means of Sharing Information with the Federal Government. The Non-Federal Entity Guidance discusses the various ways private sector entities can share information with the federal government. It particularly emphasizes four methods of sharing with the Department of Homeland Security: automated indicator sharing, web form, email, and information sharing and analysis organizations and centers. The guidance also notes that CISA permits sharing for a cybersecurity purpose with any part of the federal government, but that liability protections do not attach to sharing beyond the Department of Homeland Security (for more information, see our legal update, " Cybersecurity Information Sharing Act Signed Into US Law as Part of Omnibus Appropriations Legislation").3


The Non-Federal Entity Guidance explains the liability protections that attach to sharing through the Department of Homeland Security as discussed above (as well as to sharing among private entities) and six other protections that attach to sharing in accordance with CISA: (i) antitrust exemption; (ii) exemption from state and federal disclosure laws; (iii) exemption from certain state and federal regulatory uses; (iv) no waiver of privilege for shared material; (v) treatment of commercial, financial and proprietary information; and (vi) ex parte communications waiver.

"Privacy and Civil Liberties Interim Guidelines: Cybersecurity Information Sharing Act of 2015"

The "Privacy Guidelines" govern "the receipt, retention, use, and dissemination of cyber threat indicators by a federal entity obtained in connection with activities authorized in CISA." Final guidelines are required by June 15, 2016. The Privacy Guidelines describe the Fair Information Practice Principles (FIPPs) as "the widely accepted framework of defining principles to be used in the evaluation and consideration of systems, processes, or programs that affect individual privacy." The Privacy Guidelines provide a table describing the manner in which the FIPPs apply to the sharing of cyber threat indicators. (The FIPPs are: transparency; individual participation; purpose specification; data minimization; use limitation; data quality and integrity; security; and accountability and auditing).

As contemplated by CISA Section 105(b), the Privacy Guidelines primarily focus on cyber threat indicators. However, they "strongly" encourage federal entities "to apply the requirements found in these guidelines to defensive measures" as well. The Privacy Guidelines identify requirements related to: the receipt of information by the federal government, notifications to federal entities when a cyber threat indicator or defensive measure has been shared in error or contravention of CISA, notifications to United States persons whose information is shared in violation of CISA and the use, safeguarding, retention and dissemination of information shared pursuant to CISA. The Privacy Guidelines also discuss appropriate sanctions for violations of CISA by government employees and audit mechanisms established to assure compliance.

"Interim Procedures Related to the Receipt of Cyber Threat Indicators and Defensive Measures by the Federal Government"

The "Receipt Procedures" describe the "processes for receiving, handling, and disseminating information that is shared pursuant to CISA, including through operation of the DHS Automated Indicator Sharing capability." It explains that "[t]he DHS capability to receive, filter, analyze, and disseminate such information in real-time leverages Structured Threat Information eXpression (STIX) and Trusted Automated eXchange of Indicator Information (TAXII) specifications, along with the procedures and standards developed by the national cybersecurity centers."4 "Any entity participating in th[e] AIS capability must be able to communicate using these machine-to-machine specifications."

The Receipt Procedures also describe how DHS will filter and analyze all submitted information through automated processes, and, when necessary, human review. They go on to explain how the "sanitized" cyber threat indicators or defensive measures will be disseminated to other federal entities and to discuss similar processes for information received through a DHS web form or emails. The Receipt Procedures also explain the audit capabilities that federal entities will need to maintain to review activity conducted under CISA. Final procedures are required by June 15, 2016.

"Sharing of Cyber Threat Indicators and Defensive Measures by the Federal Government under the Cybersecurity Information Sharing Act of 2015"

The "Federal Government Procedures" "encourage[]" federal entities "to share [cyber threat indicators] and [defensive measures] as broadly and as quickly as possible." "[F]ederal entities should continuously identify and implement programs to share such [cyber threat indicators] and [defensive measures] with each other and with non-federal entities." The Federal Government Procedures describe pre-existing programs to share classified (Sec. 103(a)(1)), declassified (Sec. 103(a)(2)) and unclassified (Sec. 103(a)(3)) information with private sector entities. They also detail the process "to facilitate notifications to entities affected by malicious cyber activity" that is required under Section 103(a)(4) and that was originally created under Executive Order 13636, Improving Critical Infrastructure Cybersecurity. The Federal Government Procedures go on to highlight various federal entities that periodically disseminate cybersecurity best practices to the public. In addition, these procedures discuss the roles and responsibilities of Information Sharing and Analysis Centers and Information Sharing and Analysis Organizations.


1 Available at https://www.mayerbrown.com/Cybersecurity-Information-Sharing-Act-Signed-Into-US-Law-as-Part-of-Omnibus-Appropriations-Legislation-12-21-2015/.

2 Available at https://www.us-cert.gov/ais.

3 Available at https://www.mayerbrown.com/Cybersecurity-Information-Sharing-Act-Signed-Into-US-Law-as-Part-of-Omnibus-Appropriations-Legislation-12-21-2015/.

4 The Receipt Guidance describes STIX and TAXII in relevant detail. STIX is defined in part as: "a language for describing cyber threat information in a standard manner for the reading convenience of machines, not humans. STIX provides a common mechanism for addressing structured cyber threat information across and among this full range of use cases improving consistency, efficiency, interoperability, and overall situational awareness." TAXII, by contrast, is defined in part as: "a standard for exchanging structured cyber threat information in a trusted manner. TAXII defines services, protocols and messages to exchange cyber threat information for the detection, prevention, and mitigation of cyber threats."

Originally published on February 23, 2016

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Mayer Brown is a global legal services provider comprising legal practices that are separate entities (the "Mayer Brown Practices"). The Mayer Brown Practices are: Mayer Brown LLP and Mayer Brown Europe – Brussels LLP, both limited liability partnerships established in Illinois USA; Mayer Brown International LLP, a limited liability partnership incorporated in England and Wales (authorized and regulated by the Solicitors Regulation Authority and registered in England and Wales number OC 303359); Mayer Brown, a SELAS established in France; Mayer Brown JSM, a Hong Kong partnership and its associated entities in Asia; and Tauil & Chequer Advogados, a Brazilian law partnership with which Mayer Brown is associated. "Mayer Brown" and the Mayer Brown logo are the trademarks of the Mayer Brown Practices in their respective jurisdictions.

© Copyright 2016. The Mayer Brown Practices. All rights reserved.

This Mayer Brown article provides information and comments on legal issues and developments of interest. The foregoing is not a comprehensive treatment of the subject matter covered and is not intended to provide legal advice. Readers should seek specific legal advice before taking any action with respect to the matters discussed herein.

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