CVE-2026-46428

CRITICAL

lettre has TLS hostname verification disabled when using Boring TLS backend

Title source: cna
STIX 2.1

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 (4)

Core 4

Scores

CVSS v4 9.1
EPSS 0.0019
EPSS Percentile 9.1%
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CISA SSVC

Vulnrichment
Exploitation poc
Automatable no
Technical Impact total

Details

CWE
CWE-295
Status published
Products (2)
crates.io/lettre 0.10.1 - 0.11.22crates.io
lettre/lettre >= 0.10.1, < 0.11.22
Published Jul 20, 2026
Tracked Since Jul 20, 2026