You can use the illustrations published on unDraw for personal and commercial projects, without the need to include attribution.
The full license:
Copyright 2018 Katerina Limpitsouni
All images, assets and vectors published on unDraw can be used for free. You can use them for noncommercial and commercial purposes. You do not need to ask permission from or provide credit to the creator or unDraw.
More precisely, unDraw grants you an nonexclusive, worldwide copyright license to download, copy, modify, distribute, perform, and use the assets provided from unDraw for free, including for commercial purposes, without permission from or attributing the creator or unDraw. This license does not include the right to compile assets, vectors or images from unDraw to replicate a similar or competing service, in any form. This extends to automated ways to scrape, search or download the assets included on the website without our consent.
Brand logos that are included:
Are registered trademarks of their respected owners. Are included on a promotional basis and do not represent an association with unDraw or its users. Do not indicate any kind of endorsement of the trademark holder towards unDraw, nor vice versa. Are provided with the sole purpose to represent the actual brand/service/company that has registered the trademark and must not be used otherwise.