UNDERWRITING AGREEMENT

October 30, 2006

Credit Suisse Securities (USA) LLC

11 Madison Avenue, 4 ^th Floor

New York, New York 10010

Ladies and Gentlemen:

Credit Suisse First Boston Mortgage Securities Corp., a corporation organized and existing under the laws of the State of Delaware (the “Depositor”), proposes to sell to Credit Suisse Securities (USA) LLC (“Credit Suisse”) (the “Underwriter”) fifteen classes of the Depositor’s Home Equity Mortgage Pass-Through Certificates, Series 2006-5. Such classes have been designated as the Class A-1, Class A-2, Class A-3, Class A-IO, Class A-R, Class M-1, Class M-2, Class M-3, Class M-4, Class M-5, Class M-6, Class M-7, Class M-8, Class M-9 and Class B-1 Certificates (collectively, the “Certificates”). The Certificates, together with the Depositor’s Home Equity Mortgage Pass-Through Certificates, Series 2006-5, Class P, Class X-1, Class X-2 and Class X-S Certificates, will represent the entire beneficial ownership interest in a trust fund (the “Trust Fund”) consisting of a pool of conventional, primarily fixed rate, one-to-four family, primarily second lien residential mortgage loans (the “Initial Mortgage Loans”) having an aggregate principal balance of approximately $687,866,687 as of October 1, 2006 (the “Cut-off Date”) and amounts on deposit in the Pre-Funding Account. The Initial Mortgage Loans identified on the Mortgage Loan Schedule were originated or acquired by various mortgage loan originators and sold to DLJ Mortgage Capital, Inc. (“DLJMC”), an affiliate of the Depositor, pursuant to one or more mortgage loan purchase agreements. These Initial Mortgage Loans were subsequently transferred to the Depositor pursuant to an assignment and assumption agreement between the Depositor and DLJMC, dated as of October 31, 2006 (the “Assignment Agreement”).

The Certificates are to be issued pursuant to a Pooling and Servicing Agreement to be dated as of October 1, 2006 (the “Pooling Agreement”) among the Depositor, DLJMC, U.S. Bank National Association, as trustee (the “Trustee”), Select Portfolio Servicing, Inc., as a servicer (“SPS”) and as master servicer (the “Master Servicer”) and Ocwen Loan Servicing, LLC, as a servicer (“Ocwen” and together with SPS, the “Servicers”). The Initial Mortgage Loans will be transferred to the Trust Fund pursuant to the Pooling Agreement.

Capitalized terms used herein but not defined herein shall have the meanings provided in the Pooling Agreement.

1.   Representations and Warranties . The Depositor represents and warrants to and agrees with the Underwriter that:

(a)   The Depositor has filed with the Securities and Exchange Commission (the “Commission”) a registration statement (including a prospectus) on Form S-3 (No. 333-135481) for the registration under the Securities Act of 1933, as amended (the “Act”), of mortgage pass-through certificates issuable in series. Such registration statement has been declared effective by the Commission under the Act. Such registration statement, including exhibits thereto and any information incorporated therein by reference, as amended to the date of this Agreement, is hereinafter called the “Registration Statement,” and such prospectus, in the form in which it was last filed with the Commission, as supplemented by a prospectus supplement relating to the Certificates to be filed pursuant to Rule 424 under the Act (such prospectus supplement in the form first filed after the date hereof pursuant to Rule 424 hereinafter called the “Prospectus Supplement”), and any information incorporated therein by reference, is hereinafter collectively referred to as the “Prospectus.” The Depositor further proposes to prepare, after the final terms of all classes of the Certificates have been established, a Free Writing Prospectus that will contain substantially all information that will appear in the Prospectus Supplement, to the extent that such information is known at that time and minus specific sections including the Method of Distribution section (such Free Writing Prospectus, together with the Basic Prospectus, the “Definitive Free Writing Prospectus”). The Definitive Free Writing Prospectus must be provided to each investor prior to the time of Contract of Sale (as defined herein).

(b)   The Registration Statement, at the time it became effective (the “Effective Date”), and the prospectus contained therein, and any amendments thereof and supplements thereto filed prior to the date hereof, conformed in all material respects to the requirements of the Act and the rules and regulations of the Commission thereunder; and on the date of this Agreement and on the Closing Date (as hereinafter defined), the Registration Statement and the Prospectus, and any amendments thereof and supplements thereto, will conform in all material respects to the requirements of the Act and the rules and regulations of the Commission thereunder. The Registration Statement, at the time it became effective, did not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading; and the Prospectus, as of the date the Registration Statement became effective, as of its date and as of the date hereof, did not contain an untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the Depositor makes no representations or warranties as to either (i) any information contained in or omitted from the portions of the Prospectus set forth under the caption “Method of Distribution” relating to the Certificates and the stabilization legend required by Item 502(d)(1) under Regulation S-K of the Act (the “Underwriter Information”) or (ii) any decrement or yield tables set forth in the section titled “Yield on the Certificates” in the Prospectus Supplement (the “Decrement/Yield Tables”). In addition, the Definitive Free Writing Prospectus, as of the date thereof and as of the Closing Date, did not and will not contain an untrue statement of a material fact and did not and will not omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The effective date shall mean the earlier of the date by which the Prospectus Supplement is first used and the time of the first Contract of Sale to which such Prospectus Supplement relates.

(c)   The Certificates will conform to the description thereof contained in the Prospectus and the Certificates will on the Closing Date be duly and validly authorized; and, when validly executed, authenticated, issued and delivered in accordance with the Pooling Agreement, the Certificates will be validly issued and outstanding and entitled to the benefits of the Pooling Agreement.

(d)   The Depositor has been duly incorporated and is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation, with corporate power and authority to own, lease and operate its properties and to conduct its business as described in the Prospectus and to enter into and perform its obligations under this Agreement, the Assignment Agreement and the Pooling Agreement.

(e)   At or prior to the Closing Date, the Depositor will have entered into the Assignment Agreement with respect to the transfer of the Initial Mortgage Loans to the Depositor by DLJMC and, assuming the due authorization, execution and delivery thereof by the other parties thereto, the Assignment Agreement on the Closing Date will constitute a valid and binding agreement of the Depositor, enforceable in accordance with its terms, except as may be limited by bankruptcy, insolvency, reorganization or other laws relating to or affecting the enforcement of creditors’ rights and by general equity principles.

(f)   At or prior to the Closing Date, the Depositor will have entered into the Pooling Agreement with respect to the Certificates, and assuming the due authorization, execution and delivery thereof by the other parties thereto, the Pooling Agreement on the Closing Date will constitute a valid and binding agreement of the Depositor enforceable in accordance with its terms, except as may be limited by bankruptcy, insolvency, reorganization or other laws relating to or affecting the enforcement of creditors’ rights and by general equity principles.

(g)   Neither the issuance or sale of the Certificates nor the consummation of any other of the transactions herein contemplated, nor the fulfillment of the terms hereof, will conflict with or violate any term or provision of the certificate of incorporation or by-laws of the Depositor or any statute, order or regulation applicable to the Depositor of any court, regulatory body, administrative agency or governmental body having jurisdiction over the Depositor, and will not conflict with, result in a breach or violation or the acceleration of, or constitute a default under, the terms of any indenture or other agreement or instrument to which the Depositor is a party or by which it is bound.

(h)   This Agreement has been duly authorized, executed and delivered by the Depositor.

(i)   No consent, approval, authorization or order of any court or governmental authority or agency is required for the consummation by the Depositor of the transactions contemplated by this Agreement, except such as may be required under the Act, the Rules and Regulations or state securities or Blue Sky laws or have previously been obtained.

(j)   Immediately prior to the transfer of the Initial Mortgage Loans to the Trustee as contemplated by the Pooling Agreement, the Depositor (i) will have good title to, and will be the sole owner of, the Initial Mortgage Loans being transferred by it to the Trustee pursuant thereto, free and clear of any lien, pledge, encumbrance or other security interest (collectively, “Liens”), (ii) will not have assigned to any person any of its right, title or interest in such Initial Mortgage Loans or in the Pooling Agreement, and (iii) will have the power and authority to sell such Initial Mortgage Loans to the Trustee, and upon the execution and delivery of the Pooling Agreement by the Trustee, the Trustee will have acquired all of the Depositor’s right, title and interest in and to the Initial Mortgage Loans, and upon delivery to the Underwriter of the Certificates and payment by the Underwriter upon receipt of the Certificates, the Underwriter will have title to the Certificates free of Liens.

(k)   Neither the Depositor nor the Trust created by the Pooling Agreement is an “investment company” within the meaning of such term under the Investment Company Act of 1940, as amended (the “1940 Act”) and the rules and regulations of the Commission thereunder.

(1)   Any taxes, fees and other governmental charges in connection with the execution and delivery of this Agreement and the Pooling Agreement and the execution, issuance, delivery and sale of the Certificates which have become due or will be due on or prior to the Closing Date, shall have been or will be paid on or prior to the Closing Date.

(m)   The Depositor is not, as of the date upon which it delivers the Definitive Free Writing Prospectus, an Ineligible Issuer, as such term is defined in Rule 405 of the 1933 Act Regulations.

2.   Purchase and Sale . Subject to the terms and conditions and in reliance upon the representations and warranties herein set forth, the Depositor agrees to sell to the Underwriter, and the Underwriter agrees to purchase from the Depositor, all of the Certificates at the purchase price set forth in Schedule I hereto.

3.   Delivery and Payment . Delivery of and payment for the Certificates shall be made at 9:00 a.m. EST on October 31, 2006 which date and time may be postponed by agreement between the Underwriter and the Depositor (such date and time being herein called the “Closing Date”). The Certificates (other than the Class A-R Certificates) will be delivered in book-entry form through the facilities of The Depository Trust Company. The Class A-R Certificates will be issued in fully registered certificated form. Delivery of the Certificates shall be made to the Underwriter against payment by the Underwriter of the purchase price therefor to or upon the order of the Depositor by certified or official bank check or checks payable in federal or other immediately available funds. The Certificates shall be registered in such names and in such denominations as Credit Suisse may request not less than three full business days in advance of the Closing Date.

The Depositor agrees to notify the Underwriter at least two business days before the Closing Date of the exact principal balance evidenced by the Certificates and to have the Certificates available for inspection, checking and packaging in New York, New York, no later than 12:00 noon on the business day prior to the Closing Date.

4.   Offering by Underwriter .

(a)   It is understood that the Underwriter proposes to offer and/or solicit offers for the Certificates to be purchased by it for sale to the public as set forth in the Prospectus and the Underwriter agrees that all such offers, solicitations and sales by it shall be made in compliance with all applicable laws and regulations. Prior to the date hereof, you have not offered, pledged, sold, disposed of or otherwise transferred any Certificate or any security backed by the Mortgage Loans, any interest in any Certificate or such security or any Mortgage Loan.

(b)   It is understood that the Underwriter will solicit offers to purchase the Certificates as follows:

(1)   Prior to the time you have received the Definitive Free Writing Prospectus you may, in compliance with the provisions of this Agreement, solicit offers to purchase Certificates; provided, that you shall not accept any such offer to purchase a Certificate or any interest in any Certificate or Mortgage Loan or otherwise enter into any Contract of Sale for any Certificate, any interest in any Certificate or any Mortgage Loan prior to the investor’s receipt of Definitive Free Writing Prospectus.

(2)   Any Free Writing Prospectus (other than the Definitive Free Writing Prospectus) relating to the Certificates used by an Underwriter in compliance with the terms of this Agreement prior to the time such Underwriter has entered into a Contract of Sale for Certificates shall prominently set forth substantially the following statement:

The information in this free writing prospectus is preliminary, and will be superseded by the Definitive Free Writing Prospectus. This free writing prospectus is being delivered to you solely to provide you with information about the offering of the Certificates referred to in this free writing prospectus and to solicit an offer to purchase the Certificates, when, as and if issued. Any such offer to purchase made by you will not be accepted and will not constitute a contractual commitment by you to purchase any of the Certificates until we have accepted your offer to purchase Certificates. We will not accept any offer by you to purchase Certificates, and you will not have any contractual commitment to purchase any of the Certificates until after you have received the Definitive Free Writing Prospectus. You may withdraw your offer to purchase Certificates at any time prior to our acceptance of your offer.

“Written Communication” has the same meaning as that term is defined in Rule 405 of the 1933 Act Regulations.

(3)   Any Free Writing Prospectus relating to Certificates and used by an Underwriter in connection with marketing the Certificates, including the Definitive Free Writing Prospectus, shall prominently set forth substantially the following statement:

The Certificates referred to in these materials are being sold when, as and if issued. You are advised that Certificates may not be issued that have the characteristics described in these materials. Our obligation to sell such Certificates to you is conditioned on the mortgage loans and certificates having the characteristics described in these materials. If for any reason we do not deliver such Certificates, we will notify you, and neither the issuer nor any underwriter will have any obligation to you to deliver all or any portion of the Certificates which you have committed to purchase, and none of the issuer nor any underwriter will be liable for any costs or damages whatsoever arising from or related to such non-delivery.

(c)   It is understood that you will not enter into a Contract of Sale with any investor until the Definitive Free Writing Prospectus has been conveyed to the investor. For purposes of this Agreement, Contract of Sale has the same meaning as in Rule 159 of the 1933 Act Regulations and all Commission guidance relating to Rule 159. The Definitive Free Writing Prospectus shall prominently set forth substantially the following statement:

This Definitive Free Writing Prospectus supersedes the information in any free writing prospectus previously delivered in connection with this offering, to the extent that this Definitive Free Writing Prospectus is inconsistent with any information in any free writing prospectus delivered in connection with this offering.

(d)   It is understood that the Underwriter may prepare and provide to prospective investors certain Free Writing Prospectuses (as defined below), subject to the following conditions:

(1)   Unless preceded or accompanied by a prospectus satisfying the requirements of Section 10(a) of the Act, an Underwriter shall not convey or deliver any Written Communication to any person in connection with the initial offering of the Certificates, unless such Written Communication either (i) is made in reliance on Rule 134 under the Act, (ii) constitutes a prospectus satisfying the requirements of Rule 430B under the Act, (iii) is the Definitive Free Writing Prospectus, or (iv) both (1) constitutes a Free Writing Prospectus (as defined below) used in reliance on Rule 164 and (2) includes only information that is within the definition of ABS Informational and Computational Materials as defined in Item 1100 of Regulation AB, or Permitted Additional Materials.

(2)   The Underwriter shall comply with all applicable laws and regulations in connection with the use of Free Writing Prospectuses, including but not limited to Rules 164 and 433 of the 1933 Act Regulations and all Commission guidance relating to Free Writing Prospectuses, including but not limited to Commission Release No. 33-8591.

(3)   For purposes hereof, “Free Writing Prospectus” shall have the meaning given such term in Rules 405 and 433 of the 1933 Act Regulations. “Issuer Information” shall mean information included in a Free Writing Prospectus that both (i) is within the types of information specified in clauses (1) to (5) of footnote 271 of Commission Release No. 33-8591 (Securities Offering Reform) as shown in Exhibit C hereto and (ii) has been either prepared by, or has been reviewed and approved by, the Depositor. “Underwriter Derived Information” shall refer to information of the type described in clause (5) of such footnote 271 when prepared by an Underwriter. “Permitted Additional Materials” shall mean information that is not ABS Informational and Computational Materials and (x) that are referred to in Section 4(d)(12)), (y) that constitute Certificate price, yield, weighted average life, subscription or allocation information, or a trade confirmation, or (z) otherwise with respect to which the Depositor has provided written consent to the Underwriter to include in a Free Writing Prospectus. As used herein with respect to any Free Writing Prospectus, “Pool Information” means the information with respect to the characteristics of the Mortgage Loans and administrative and servicing fees, as provided by or on behalf of the Depositor to the Underwriter at the time most recent to the date of such Free Writing Prospectus.

(4)   All Free Writing Prospectuses provided to prospective investors, whether or not filed with the Commission, shall bear a legend including substantially the following statement:

“THE DEPOSITOR HAS FILED A REGISTRATION STATEMENT (INCLUDING A PROSPECTUS) WITH THE SEC FOR THE OFFERING TO WHICH THIS COMMUNICATION RELATES. BEFORE YOU INVEST, YOU SHOULD READ THE PROSPECTUS IN THAT REGISTRATION STATEMENT AND OTHER DOCUMENTS THE ISSUER HAS FILED WITH THE SEC FOR MORE COMPLETE INFORMATION ABOUT THE ISSUER AND THE OFFERING. YOU MAY GET THESE DOCUMENTS AT NO CHARGE BY VISITING EDGAR ON THE SEC WEB SITE AT WWW.SEC.GOV [AT “_______________________”, OR AT UNDERWRITER WEBSITE]. ALTERNATIVELY, THE ISSUER, ANY UNDERWRITER OR ANY DEALER PARTICIPATING IN THE OFFERING WILL ARRANGE TO SEND YOU THE PROSPECTUS AT NO CHARGE IF YOU REQUEST IT BY CALLING TOLL-FREE 1-8XX-XXX-XXXX OR VIA E-MAIL AT ________________________.

The Depositor shall have the right to require additional specific legends or notations to appear on any Free Writing Prospectus, the right to require changes regarding the use of terminology and the right to determine the types of information appearing therein with the approval of the Underwriter (which shall not be unreasonably withheld).

(5)   The Underwriter shall deliver to the Depositor and its counsel (in such format as required by the Depositor) prior to the proposed date of first use thereof, (i) any Free Writing Prospectus prepared by or on behalf of the Underwriter that contains any information that, if reviewed and approved by the Depositor, would be Issuer Information, and (ii) any Free Writing Prospectus or portion thereof prepared by the Underwriter that contains only a description of the final terms of the Certificates after such terms have been established for all classes of Certificates being publicly offered. No information in any Free Writing Prospectus (other than the Definitive Free Writing Prospectus) shall consist of information of a type that is not included within the definition of ABS Informational and Computational Materials, or is not Permitted Additional Materials. To facilitate filing to the extent required by Section 5(b) or 4(f), as applicable, all Underwriter Derived Information shall be set forth in a document separate from the document including Issuer Information. All Free Writing Prospectuses described in this subsection (5) must be approved by the Depositor before the Underwriter provides the Free Writing Prospectus to investors pursuant to the terms of this Agreement. Notwithstanding the foregoing, the Underwriter shall not be required to deliver any Free Writing Prospectus to the extent that it does not contain substantive changes from or additions to any Free Writing Prospectus previously approved by the Depositor.

(6)   The Underwriter shall provide the Depositor with a letter from Deloitte & Touche LLP, certified public accountants, prior to the Closing Date, with respect to any Free Writing Prospectus provided by the Underwriter to the Depositor under Section 4(d)(5), satisfactory in form and substance to the Depositor and their counsel and the Underwriter, to the effect that such accountants have performed certain specified procedures, all of which have been agreed to by the Depositor and the Underwriter, as a result of which they determined that all accounting, financial or statistical information that is included in such Free Writing Prospectus, is accurate except as to such matters that are not deemed by the Depositor and the Underwriter to be material. The foregoing letter shall be at the expense of the respective Underwriter.

(7)   None of the information in the Free Writing Prospectuses may conflict with the information contained in the Prospectus or the Registration Statement.

(8)   The Depositor shall not be obligated to file any Free Writing Prospectuses that have been determined to contain any material error or omission, unless the Depositor is required to file the Free Writing Prospectus pursuant to Section 5(b) below. In the event that an Underwriter becomes aware that, as of the date on which an investor entered into an agreement to purchase any Certificates, any Free Writing Prospectus prepared by or on behalf of the Underwriter and delivered to such investor contained