CVE-2026-46428: 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 h

unknownCVE-2026-46428

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: unknown
Published: 2026-07-20
Last updated: 2026-07-23
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-46428

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-464280.19% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 9% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-46428	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

criticalGHSA-4pj9-g833-qx53: lettre has TLS hostname verification disabled when using Boring TLS backendghsa

Recent advisories for lettre is a

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

criticalGHSA-4pj9-g833-qx53: lettre has TLS hostname verification disabled when using Boring TLS backendghsa · 2026-07-28