Exhibit 5.1

Yigal Arnon (1929-2014) Dror Vigdor Amalia Meshi Amnon Lorch Hagai Shmueli Barry Levenfeld David H. Schapiro Hagit Bavly Orna Sasson Barak Tal Shiri Shaham Doron Tamir Daniel Abarbanel David Osborne Gil Oren Ronit Amir Orly Tsioni Mordehai Baicz Barak Platt Benjamin Horef Yoran Gill Asaf Eylon Daniel Marcovici Adrian Daniels Yuval Shalheveth Jacob Ben Chitrit Peter Sugarman Ben Sandler Boaz Fiel Joeri Kreisberg Simon Weintraub Ruth Loven Yarom Romem Adam Spruch Yuval Bargil Eliran Furman Eran Lempert Ofir Levy
Daniel Green Hanital Belinson Yoheved Novogroder
Oren Roth
Dror Varsano Odelia Sidi Shira Lahat Ido Chitman Noa Afik Aner Hefetz David Akrish Nir Rosner Assaf Mesica Liron Hacohen Guy Fuhrer Ezra Gross David Roness Eli Greenbaum Lee Maor
Nimrod Vromen Guy Sagiv Micha Tollman Shani Rapoport Lior Gelbard Michal Sagmon Hila Roth Keren Tal Neta Goshen Roy Masuri Eyal Yacoby
Daphna Livneh Tamar Gilboa Yael Hoefler Sagi Schiff Lilach Grimberg Adi Samuel Netanella Treistman Daniel Damboritz Shlomi Schneider Alona Toledano
Elad Offek Yuval Shamir Dana Heller Adi Tal
Yulia Lazbin Joshua Lieberman
Liat Pillersdorf Orly Rottenberg
Avi Anouchi Shay Fahima
Sivan Gilron Dotan Naftali Nir
Tomer Bar-Nathan
Evan Schendler
Lihi Katzenelson Eyal Aichel Shahar Uziely Edan Regev
Yehudit Biton Ohad Shalem Gitit Ramot-Adler
Omri Schnaider Rinat Michael
Adi Attar
Ivor Krumholtz Daniella Milner
Harel Sinai Amos Oseasohn Guy Kortany Goor Koren
Adi Daniel
Dafna Shaham 
Miriam Friedmann Itamar Lippner Ricki Newman
Roni Osborne Ortal Zanzuri Reut Sasson
Josh Hersch
Roey Sasson Shir Eshkol Nir Rodnizky Noa Slavin
Guy Fatal
Shani Lorch
Ira Burshtein Elichai Bitter Amir Weiser Itamar Cohen
Shai Margalit Yossi Paloch
Ofir Schwartz
Meital Singer Yonatan Whitefield Moshe Lankry Shira Teger Rachel Lerman Ravid Saar Debbie Shalit Sophie Blackston
Eti Elbaz Hagar Mizrachi
Elad Morgenstern
Ron Ashkenazi Dafna Raz Sara Haber
Erez Leibovich Ilan Akouka Shlomit Bukaya Yehonatan Cohen David Shmulevitz Tair Cherbakovsky Ophir Dagan
Yael Meretyk Hanan Dov Ehrman
Nataly Damary
Noam Pratzer Nava Rozolyo Shiran Glitman Dor Daniel Michael Rosenblit Heni Rothstein-Cohen Dani Weissberg Lareine Khoury Nohar Hadar Shirley Youseri Nitzan Kahana Yahel Kaplan Liad Kalderon Daniel Szriber Shachar Hindi Natalie Korenfeld Moshe Pasker Mazi Ohayon Nitzan Fisher-Conforti Victoria Savu
Derora Tropp Rotem Bar Ner Rebecca Hazan Of Counsel
Roy Keidar Of Counsel Paul H. Baris (1934-2010) Rami Kook Nira Kuritzky Eran Ilan

Tel-Aviv, February 15, 2018

Cyren Ltd.

Ladies and Gentlemen:

We refer to the Registration Statement on Form S-8 (the “Registration Statement”) to be filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Securities Act”), on behalf of Cyren Ltd., a company organized under the laws of the State of Israel (the “Company”), for the purpose of registering under the Securities Act 4,600,000 of the Company’s Ordinary Shares, nominal value NIS 0.15 per share (the “Shares”), available for issuance under the Cyren Ltd. 2016 Non-Employee Director Equity Incentive Plan and the Cyren Ltd. 2016 Equity Incentive Plan (together, the “Plans”).

In rendering an opinion on the matters hereinafter set forth, we have assumed the authenticity of all original documents submitted to us as certified, conformed or photographic copies thereof, the genuineness of all signatures and the due authenticity of all persons executing such documents. We have assumed the same to have been properly given and to be accurate, we have assumed the truth of all facts communicated to us by the Company, we have assumed that all consents, minutes and protocols of meetings of the Company's board of directors and shareholders meetings of the Company which have been provided to us are true, accurate and have been properly prepared in accordance with the Company's incorporation documents and all applicable laws, and we have also assumed the compliance of any grant of Shares with the Company's compensation policy, as in effect from time to time.

As outside Israeli counsel to the Company, we have performed such investigations, and have examined such corporate records, certificates and other documents, and such questions of law, as we have considered necessary or appropriate for the purpose of our opinion. Upon the basis of such examination, we are of the opinion that, the Shares have been duly and validly authorized for issuance and, when issued in accordance with the applicable grant or option agreement, pursuant to the terms of the Plans and in accordance with the Registration Statement, the Shares will be legally and validly issued, fully paid and non-assessable.

1 Azrieli Center, Tel Aviv, 6702101   |   Phone: +972-3-6087777   |   Fax: +972-3-6087724

31 Hillel Street, Jerusalem, 9458131   |   Phone: +972-2-6239239   |   Fax: +972-2-6239233

www.arnon.co.il   |   info@arnon.co.il

The above opinion is based on facts existing on the date hereof and of which we are aware. We express no opinion as to any laws other than the laws of the State of Israel as the same are in force on the date hereof and we have not, for purpose of giving this opinion, made any investigation of the laws of any other jurisdiction. This opinion is limited to the matters stated herein and no opinion is implied or may be inferred beyond the matters expressly stated.

We consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the Rules and Regulations of the Commission thereunder.

Very truly yours,

/s/ Yigal Arnon & Co

Yigal Arnon & Co.

1 Azrieli Center, Tel Aviv, 6702101   |   Phone: +972-3-6087777   |   Fax: +972-3-6087724

31 Hillel Street, Jerusalem, 9458131   |   Phone: +972-2-6239239   |   Fax: +972-2-6239233

www.arnon.co.il   |   info@arnon.co.il

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