The only vulnerability of Tor, which heavily depends on cryptography, is timing analysis.
One of the most important lessons of cryptography is that it doesn't exist in a vacuum. Timing between messages and message sizes can be enough to end you.
David Brumley and Dan Boneh, "Remote Timing Attacks Are Practical." In Proc. USENIX Security Symposium, 2003. https://crypto.stanford.edu/~dabo/papers/ssl-timing.pdf
Abstract
Timing attacks are usually used to attack weak computing devices such as smartcards. We show that timing attacks apply to general software systems. Specifically, we devise a timing attack against OpenSSL. Our experiments show that we can extract private keys from an OpenSSL-based web server running on a machine in the local network. Our results demonstrate that timing attacks against network servers are practical and therefore all security systems should defend against them.