CVE-2026-46428
TLS hostname verification disabled when using Boring TLS backend
Description
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. The bug was introduced in v0.10.1 and persists through v0.11.21 (latest).
How to fix CVE-2026-46428
To remediate CVE-2026-46428, upgrade the affected package to a fixed version below.
- crates.io/lettre—upgrade to 0.11.22 or later
Is CVE-2026-46428 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-46428.
Affected packages (1)
- >= 0.10.1, < 0.11.22
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 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 |