What libraries are secure to use in Cairo?

While not all (if any) libraries available for StarkNet's contract have been audited, it is important to make use of battle tested and trustworthy libraries. StarkNet has a pretty tight community, so when in doubt, ask on Discord, on one of the many telegram groups or Newton, and other devs will be able to guide you on choosing the best libraries.

As usual, the most reputable and useful collection of libraries is OpenZeppelin's cairo-contract. For any other need, have a look at Cairo Goldmine.

As the ecosystem matures, we will surely see more and more libraries being audited and this will allow a more standardised way of writing smart contracts. In the meantime, when in doubt, always ask your fellow developers/security engineers.