Government support schemes like Help to Buy have helped to inject new life into the housing market by boosting the flow of mortgage deals available for people with deposits as low as 5% saved.
But there have also been suggestions that would-be buyers are feeling more under pressure to get on the property ladder amid strong house price increases in some areas.
The CML's latest figures indicate that first-time buyers have recently been stretching themselves further with their mortgage borrowing. First-time buyers typically borrowed 3.43 times their gross income in December last year, edging up slightly from a ratio of 3.38 in November.
The MAS is an independent body set up by Government and funded by a levy on the financial services industry.
Caroline Rookes, CEO of the service, said: "It's really concerning to hear so many recent first-time buyers have over-stretched themselves financially.
"I urge all home buyers - even those higher up the property ladder - to ensure they are not taking on too much if they've borrowed the maximum available.
"Being able to afford the mortgage doesn't mean you can necessarily afford the home - and all the associated costs."
The research surveyed 974 people from the UK who had bought their first home in the last two years.
New rules are set to come into force in April which will mean lenders have to carry out more checks to work out whether people can really afford the mortgage they want to take out.
The Mortgage Market Review rules mean that lenders will have to consider whether a borrower would still be comfortable making their mortgage payments following a rise in interest rates.
