CVE-2026-46428: Cert Validation Flaw

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.

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Weakness Type (CWE)

CWE-295 CWE-295

References

Other References

https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35 https://github.com/lettre/lettre/releases/tag/v0.11.22 https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53 https://rustsec.org/advisories/RUSTSEC-2026-0141.html

Frequently Asked Questions

What is CVE-2026-46428? +

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.

How do I check if I'm vulnerable to CVE-2026-46428? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-46428