Unassociated Document

May 13, 2014

Finjan Holdings, Inc.

122 East 42nd Street, Suite 1512

New York, New York 10168

Ladies and Gentlemen:

We have acted as counsel to Finjan Holdings, Inc., a Delaware corporation (the “Company”), in connection with the filing of a Registration Statement on Form S-8 (the “Registration Statement”) for the registration under the Securities Act of 1933, as amended (the “Act”), of the issuance and sale by the Company of 2,236,836 shares (the “Shares”) of the Company’s common stock, $0.0001 par value per share (the “Common Stock”), pursuant to the Finjan Holdings, Inc. 2013 Global Share Option Plan (the “Plan”). This opinion is being furnished in accordance with the requirements of Item 601(b)(5) of Regulation S-K under the Act.

In connection with this opinion, we have relied as to matters of fact, without investigation, upon certificates of public officials and others and upon affidavits, certificates and written statements of directors, officers and employees of, and the accountants for, the Company. We have also examined and relied upon originals or copies, certified or otherwise identified to our satisfaction, of the following:

The Certificate of Incorporation of the Company, as amended on or before the date hereof;

The Bylaws of the Company;

Records of proceedings and actions of the Board of Directors, committees thereof and stockholders of the Company relating to the Plan;

The Plan; and

Such other instruments, documents, statements and records of the Company and others as we have deemed relevant and necessary to examine and rely upon for the purpose of this opinion.

AUSTIN CENTURY CITY CHARLOTTE CHICAGO HOUSTON IRVING LOS ANGELES

NEW YORK ORANGE COUNTY SAN FRANCISCO BAY AREA SHANGHAI WASHINGTON, DC

LONDON: KATTEN MUCHIN ROSENMAN UK LLP

A limited liability partnership including professional corporations

Finjan Holdings, Inc.

May 13, 2014

Page 2 of 2

In connection with this opinion, we have assumed the legal capacity of all natural persons, the accuracy and completeness of all documents and records that we have reviewed, the genuineness of all signatures, the due authority of the parties signing such documents, the authenticity of the documents submitted to us as originals and the conformity to authentic original documents of all documents submitted to us as certified, conformed or reproduced copies. We have also assumed that, at the time of issuance of the Shares, (i) any and all agreements related to the issuance of the Shares under the Plan will conform to the terms and conditions of the Plan, and will have been duly executed and delivered by the Company and, as applicable, the recipients of the Shares, (ii) the Committee (as defined in the Plan) will have approved the issuance of awards of the Shares pursuant to the Plan, and (iii) any cash consideration payable to the Company in connection with any issuance of the Shares will not be less than the par value per share of the Common Stock.

Based upon and subject to the foregoing, it is our opinion that, when the Shares are issued and delivered by the Company and (to the extent applicable) paid for in accordance with the terms of the Plan and the relevant award agreements, the Shares will be validly issued, fully paid and nonassessable.

Our opinion expressed above is limited to the General Corporation Law of the State of Delaware, and we do not express any opinion concerning any other laws. This opinion is given as of the date hereof and we assume no obligation to advise you of changes that may hereafter be brought to our attention.

We hereby consent to the filing of this opinion with the Securities and Exchange Commission as an exhibit to the Registration Statement. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Securities and Exchange Commission.

Very truly yours,

/s/ Katten Muchin Rosenman LLP

KATTEN MUCHIN ROSENMAN LLP