CVE-2026-46428
lettre has TLS hostname verification disabled when using Boring TLS backend
- State
- Published
- Severity
- 9.1 Critical
- Published
- Jul 20, 2026
- Updated
- Jul 21, 2026
- Reserved
- May 13, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.1 Critical | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N | GitHub_M |
Weaknesses
- CWE-295 Improper Certificate Validation
Affected Products
| Product | Versions |
|---|---|
lettrelettre |
|
References
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