Freelancer.com's User Agreement(1) covers basic conduct such as not to use content that infringes upon an existing copyright, patent, intellectual property right, proprietary right or right of privacy.
(1) Link to https://www.freelancer.com/about/terms
In addition, there's also aFreelancer Code of Conduct(2) which includes expectations from the contractors, such as the requirement to keep confidentiality of the projects.
(2) Link to https://www.freelancer.com/info/codeofconduct.php
Upwork
Every employer and contractor that uses Upwork to create or fulfil a contract is required to agree to itsUser Agreement(3).
Clause 15 of theUser Agreement(3) specifically refers to confidentiality.
(3) Link to https://www.upwork.com/legal/
Clause 15.1 requires mutual confidentiality from both the freelancer and employer, depending on whoever is receiving confidential information.
These clauses are genericand might be adequate for information where confidentiality is not of particular importance.
But it does not provide the full coverage of a standard non-disclosure agreement.