by Kastro
Paper/Archive/CVE-2026-46428

CVE-2026-46428

lettre lettre — lettre has TLS hostname verification disabled when using Boring TLS backend

EPSS 0.3%public exploitCVSS 9.1
critical.is priorityof 100
42
CVSS 9.1 (CNA)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 24.9.249 × 205.0Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
lettre>= 0.10.1, < 0.11.22–CNA

Scores by source

GitHub_M (CNA)9.1CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N
CISA ADPSSVCExploitation: poc · Automatable: no · Technical impact: total

References

exploitgithub.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53refgithub.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35refgithub.com/lettre/lettre/releases/tag/v0.11.22refrustsec.org/advisories/RUSTSEC-2026-0141.html