Critical 9.1Published Jul 20, 2026

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

Updated under an hour ago (Oct 26, 2026, 11:00 AM ET)

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Every CVE for lettre

Exploited in the last 30 days

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.

CVSS: 9.1 CRITICAL (v4.0, CNA)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
Weakness (CWE): CWE-295
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Jul 21, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

lettre lettre lettre:lettre (from the name)	from 0.10.1, < 0.11.22	CNA record

References

https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53x-refsource-confirm
https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35x-refsource-misc
https://github.com/lettre/lettre/releases/tag/v0.11.22x-refsource-misc
https://rustsec.org/advisories/RUSTSEC-2026-0141.htmlx-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.