Rustls: Session Debug formatting exposes TLS master secrets and resumption PSKs

Overview

Summary

Formatting a client session value with Debug exposes its TLS 1.2 master secret or TLS 1.3 resumption PSK. A custom session store that logs these values can disclose keys to readers of the logs. Ordinary connection and built-in cache diagnostics remain redacted, and the session-store interface already warns that its values are sensitive.

Details

Derived formatters traverse the session's secret-bearing fields. This conflicts with the project's explicit key-material redaction policy.

Proof of concept

Custom ClientSessionStore implementations could leak secret data by using the provided Tls12ClientSessionValue or Tls13ClientSessionValue in a way that triggers its implementation of the Debug trait.

Impact

Such store implementations could leak the master secret for the TLS connection.

Acknowledgement

Thanks to OpenAI [email protected] for the disclosure.

Affected packages

• rustls < 0.23.46
• rustls >= 0.24.0-dev.1, < 0.24.0-dev.2

Remediation

Upgrade to a patched release:

• rustls 0.23.46
• rustls 0.24.0-dev.2