Due to a non-constant-time implementation, information about the private key is leaked through timing information which is observable over the network. An attacker may be able to use that information to recover the key.
The Marvin Attack is a timing sidechannel vulnerability which allows performing RSA decryption and signing operations as an attacker with the ability to observe only the time of the decryption operation performed withthe private key. A recent survey of RSA implementations found that the Rust rsa crate is one of many implementations vulnerable to this attack. No fixed version is available at this time.