Certificate No Cut-off Date : May 1, 2001 First Distribution Date : June 25, 2001 Initial Notional Amount of this Certificate ("Denomination") : Initial Class Notional Amount of all Certificates of this Class : Percentage Interest : CUSIP : Pass-Through Rate : Maturity Date : CREDIT SUISSE FIRST BOSTON MORTGAGE SECURITIES CORP. CSFB ABS Trust Series 2001-HE12 CSFB Mortgage Pass-Through Certificates, Series 2001-HE12 Class A-IO evidencing a percentage interest in the distributions allocable to the Certificates of the above-referenced Class with respect to a Trust Fund consisting primarily of a pool of fixed rate and adjustable rate conventional mortgage loans (the "Mortgage Loans") secured by first liens on one- to four-family residential properties. Credit Suisse First Boston Mortgage Securities Corp., as Depositor This Certificate does not evidence an obligation of, or an interest in, and is not guaranteed by the Depositor, the Seller, the Servicer or the Trustee referred to below or any of their respective affiliates. Neither this Certificate nor the Mortgage Loans are guaranteed or insured by any governmental agency or instrumentality. This certifies that CEDE & CO. is the registered owner of the Percentage Interest evidenced by this Certificate (obtained by dividing the denomination of this Certificate by the aggregate of the denominations of all Certificates of the Class to which this Certificate belongs) in certain monthly distributions with respect to a Trust Fund consisting primarily of the Mortgage Loans deposited by Credit Suisse First Boston Mortgage Securities Corp. (the "Depositor"). The Trust Fund was created pursuant to a Pooling and Servicing Agreement dated as of the Cut-off Date specified above (the "Agreement") among the Depositor, DLJ Mortgage Capital, Inc., as seller (in such capacity, "Seller"), Calmco Servicing L.P., as servicer (in such capacity, "Servicer") and U.S. Bank National Association, as trustee (the "Trustee"). To the extent not defined herein, the capitalized terms used herein have the meanings assigned in the Agreement. This Certificate is issued under and is subject to the terms, provisions and conditions of the Agreement, to which Agreement the Holder of this Certificate by virtue of the acceptance hereof assents and by which such Holder is bound. Reference is hereby made to the further provisions of this Certificate set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place. This Certificate shall not be entitled to any benefit under the Agreement or be valid for any purpose unless manually countersigned by an authorized signatory of the Trustee.
