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CVE-2026-46428— lettre has TLS hostname verification disabled when using Boring TLS backend

Quick assessment

Affected
lettre lettre
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

lettre是lettre个人开发者开源的一套电子邮件发送库。 lettre 0.10.1版本至0.11.22之前版本存在加密问题漏洞，该漏洞源于boring-tls集成中的倒布尔错误导致TLS主机名验证被静默禁用，可能允许路径上的攻击者使用任何域的有效证书拦截SMTP提交，包括PLAIN/LOGIN凭据和消息内容。

AI Predicted 9.8 Difficulty: Easy EPSS 0.32% · P23

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
lettre lettre >= 0.10.1, < 0.11.22 affected
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I. Basic Information for CVE-2026-46428

Vulnerability Information
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Vulnerability Title
lettre has TLS hostname verification disabled when using Boring TLS backend
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
lettre 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
lettre是lettre个人开发者开源的一套电子邮件发送库。 lettre 0.10.1版本至0.11.22之前版本存在加密问题漏洞，该漏洞源于boring-tls集成中的倒布尔错误导致TLS主机名验证被静默禁用，可能允许路径上的攻击者使用任何域的有效证书拦截SMTP提交，包括PLAIN/LOGIN凭据和消息内容。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
lettre lettre >= 0.10.1, < 0.11.22 -

II. Public POCs for CVE-2026-46428

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III. Intelligence Information for CVE-2026-46428

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Patches & Fixes for CVE-2026-46428 (2)

Vendor Advisories for CVE-2026-46428 (2)

IV. Related Vulnerabilities

Same weakness: CWE-295

V. Comments for CVE-2026-46428

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