CVE-2026-46428
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% of all known CVEs
Summary
An inverted-boolean bug in lettre's `boring-tls` integration (versions 0.10.1 to 0.11.21) silently disables TLS hostname verification for callers using the default (strict) configuration. An on-path attacker can present any chain-valid certificate for any domain and intercept SMTP submission, including PLAIN/LOGIN credentials and message contents. Other TLS backends (native-tls, rustls) are unaffected. Version 0.11.22 patches the issue.
Risk Assessment
An attacker can intercept credentials and email content, posing a serious threat to communication confidentiality.
Recommendation
Update the lettre library to version 0.11.22 or later if you use the `boring-tls` feature.
Original NVD description (English source)
lettre is a a mailer library for Rust. Starting in version 0.10.1 and prior to version 0.11.22, an inverted-boolean bug in lettre's `boring-tls` integration silently disables TLS hostname verification for callers using the default (strict) configuration. An on-path attacker presenting any chain-valid certificate for any domain can intercept SMTP submission, including PLAIN/LOGIN credentials and message contents, against any lettre user built with the `boring-tls` feature. Other TLS backends (`native-tls`, `rustls`) are unaffected. Version 0.11.22 patches the issue.