Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

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CVE-2026-46428

Severity CVSS v4.0:
CRITICAL
Type:
CWE-295 Improper Certificate Validation
Publication date:
20/07/2026
Last modified:
20/07/2026

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.

Impact

Vector 4.0
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 CVSS v4.0 Severity and Metrics:

Base Score: 9.10 CRITICAL
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

Attack Vector (AV): Network
Attack Complexity (AC): Low
Attack Requirements (AT): Present
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): High
Integrity (VI): High
Availability (VA): None
Confidentiality (SC): Low
Integrity (SI): Low
Availability (SA): None

Base Score 4.0
9.10
Severity 4.0
CRITICAL

References to Advisories, Solutions, and Tools