matrix-sdk-crypto contains a log exposure of private key of the server-side key backup

Vulnerability Description

The matrix-sdk-crypto crate, part of the Matrix Rust SDK project, is an implementation of a Matrix end-to-end encryption state machine in Rust. In Matrix, the server-side `key backup` stores encrypted copies of Matrix message keys. This facilitates key sharing between a user's devices and provides a redundant copy in case all devices are lost. The key backup uses asymmetric cryptography, with each server-side key backup assigned a unique public-private key pair. Due to a logic bug introduced in commit 71136e44c03c79f80d6d1a2446673bc4d53a2067, matrix-sdk-crypto version 0.7.0 will sometimes log the private part of the backup key pair to Rust debug logs (using the `tracing` crate). This issue has been resolved in matrix-sdk-crypto version 0.7.1. No known workarounds are available.

References

• https://github.com/matrix-org/matrix-rust-sdk/security/advisories/GHSA-9ggc-845v-gcgv
• https://github.com/matrix-org/matrix-rust-sdk/commit/71136e44c03c79f80d6d1a2446673bc4d53a2067
• https://github.com/matrix-org/matrix-rust-sdk/commit/fa10bbb5dd0f9120a51aa1854cec752e25790bb0
• https://crates.io/crates/matrix-sdk-crypto/0.7.1
• https://github.com/matrix-org/matrix-rust-sdk/releases/tag/matrix-sdk-crypto-0.7.1