critical9.1
CVE-2026-46428
lettre has TLS hostname verification disabled when using Boring TLS backend
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | lettre | >= 0.10.1, < 0.11.22 | 0.11.22 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-4pj9-g833-qx53
- https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53
- https://nvd.nist.gov/vuln/detail/CVE-2026-46428
- https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35
- https://github.com/lettre/lettre/releases/tag/v0.11.22
- https://rustsec.org/advisories/RUSTSEC-2026-0141.html