CVE-2026-46428

critical

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.

References

https://rustsec.org/advisories/RUSTSEC-2026-0141.html

https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53

https://github.com/lettre/lettre/releases/tag/v0.11.22

https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35

Details

Source: Mitre, NVD

Published: 2026-07-20

Updated: 2026-07-21

Risk Information

CVSS v2

Base Score: 5.8

Vector: CVSS2#AV:N/AC:M/Au:N/C:P/I:P/A:N

Severity: Medium

CVSS v3

Base Score: 7.4

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Severity: High

CVSS v4

Base Score: 9.1

Vector: 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

Severity: Critical

EPSS

EPSS: 0.00191