DBRS Rates Credit Suisse First Boston Mortgage Securities Corp., CSMC Series 2009-6R

DBRS has today assigned the following ratings to the Credit Suisse First Boston Mortgage Securities Corp. (CSMC) Series 2009-6R certificates issued by CSMC Series 2009-6R (the Trust).

• $16.1 million Class 1-A1* rated at AAA

• $2.5 million Class 1-A2 rated at A

• $1.4 million Class 1-A3 rated at BBB

• $1.2 million Class 1-A4 rated at BB

• $920,000 Class 1-A5 rated at B

• $12.9 million Class 1-A7** rated at AAA

• $3.2 million Class 1-A8** rated at AAA

• $25.1 million Class 2-A1* rated at AAA

• $4.0 million Class 2-A2 rated at A

• $2.6 million Class 2-A3 rated at BBB

• $1.5 million Class 2-A4 rated at BB

• $2.3 million Class 2-A5 rated at B

• $20.1 million Class 2-A7** rated at AAA

• $5.0 million Class 2-A8** rated at AAA

• $10.3 million Class 3-A1 rated at AAA

• $1.5 million Class 3-A2 rated at A

• $531,000 Class 3-A3 rated at BBB

• $398,000 Class 3-A4 rated at B

• $5.9 million Class 4-A1 rated at AAA

• $1.2 million Class 4-A2 rated at A

• $1.0 million Class 4-A3 rated at BBB

• $840,000 Class 4-A4 rated at BB

• $945,000 Class 4-A5 rated at B

• $8.6 million Class 5-A1 rated at AAA

• $1.2 million Class 5-A2 rated at A

• $549,000 Class 5-A3 rated at BBB

• $330,000 Class 5-A4 rated at B

• $12.4 million Class 6-A1* rated at AAA

• $2.0 million Class 6-A2 rated at A

• $1.3 million Class 6-A3 rated at BBB

• $1.1 million Class 6-A4 rated at BB

• $743,000 Class 6-A5 rated at B

• $9.9 million Class 6-A7** rated at AAA

• $2.5 million Class 6-A8** rated at AAA

• $9.1 million Class 7-A1 rated at AAA

• $1.3 million Class 7-A2 rated at A

• $581,000 Class 7-A3 rated at BBB

• $348,000 Class 7-A4 rated at B

• $16.3 million Class 8-A1* rated at AAA

• $2.2 million Class 8-A2 rated at A

• $1.3 million Class 8-A3 rated at BBB

• $1.1 million Class 8-A4 rated at BB

• $440,000 Class 8-A5 rated at B

• $13.0 million Class 8-A7** rated at AAA

• $3.3 million Class 8-A8** rated at AAA

• $8.8 million Class 9-A1 rated at AAA

• $1.3 million Class 9-A2 rated at A

• $593,000 Class 9-A3 rated at BBB

• $593,000 Class 9-A4 rated at B

• $7.6 million Class 10-A1 rated at AAA

• $1.1 million Class 10-A2 rated at A

• $1.0 million Class 10-A3 rated at BBB

• $1.4 million Class 10-A4 rated at BB

• $756,000 Class 10-A5 rated at B

• $16.5 million Class 11-A1* rated at AAA

• $1.9 million Class 11-A2 rated at A

• $1.5 million Class 11-A3 rated at BBB

• $857,000 Class 11-A4 rated at B

• $13.2 million Class 11-A6** rated at AAA

• $3.3 million Class 11-A7** rated at AAA

• $23.6 million Class 12-A1* rated at AAA

• $3.1 million Class 12-A2 rated at A

• $1.9 million Class 12-A3 rated at BBB

• $931,000 Class 12-A4 rated at BB

• $621,000 Class 12-A5 rated at B

• $18.9 million Class 12-A7** rated at AAA

• $4.7 million Class 12-A8** rated at AAA

The AAA ratings on the Class A1 certificates in each group reflect the credit enhancement provided by subordination. The ratings also reflect the quality of the underlying assets, which are senior residential mortgage pass-through certificate. The Class A1A and A1B certificates (Initial Exchangeable Certificates) in the applicable groups are exchangeable for certain other classes of certificates (Exchangeable Certificates) and vice versa, in the combinations described in Annex II of the offering memorandum.

DBRS does not rate the most subordinate class within each group or Class R.

Interest and principal payments on the certificates will be made generally on the 25th day of each month commencing in June 2009. Within each group, interest payments will be distributed on a pro rata basis to the certificates, and principal will be distributed on a sequential basis to the certificates, in numerical order, until the certificate principal balances thereof are reduced to zero.

Any losses realized from the underlying securities will be allocated in a reverse numerical order to the certificates within each group.

The Trust is a resecuritization of 12 residential mortgage pass-through certificates, which are backed by pools of primarily prime fixed-rate mortgages secured by first liens on one- to four-family properties.

Notes:

• Denotes Initial Exchangeable Certificate.
  ** Denotes Exchangeable Certificate.

All figures are in U.S. dollars unless otherwise noted.

The applicable methodology is Rating U.S. Residential Mortgage-Backed Securities Transactions, which can be found on our website under Methodologies.

This is a Structured Finance rating.