httpsig-rs is a Rust implementation of IETF RFC 9421 http message signatures. Prior to version 0.0.19, the HMAC signature comparison is not timing-safe. This makes anyone who uses HS256 signature verification vulnerable to a timing attack that allows the attacker to forge a signature. Version 0.0.19 fixes the issue.
Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.