PT-2026-61618 · Lettre · Lettre

CVE-2026-46428 · Published 2026-05-14 · Updated 2026-07-20

Positive Technologies (AI Summary)

CVSS v4.0

9.1

Critical

Base vector

AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N

Name of the Vulnerable Software and Affected Versions lettre versions 0.10.1 through 0.11.21

Description An inverted-boolean bug in the boring-tls integration silently disables TLS hostname verification for users employing the default strict configuration. This allows an on-path attacker with a chain-valid certificate for any domain to intercept SMTP submission, which may include message contents and PLAIN/LOGIN credentials. This issue specifically affects users who build the library with the boring-tls feature; other TLS backends such as native-tls and rustls are not impacted.

Recommendations Update to version 0.11.22.

Exploit

Fix

Improper Certificate Validation

Weakness Enumeration

CWE-295

Related Identifiers

CVE-2026-46428

GHSA-4PJ9-G833-QX53

RUSTSEC-2026-0141

Affected Products

Lettre

References · 10

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46428.json · Exploit
• https://osv.dev/vulnerability/CVE-2026-46428 · Vendor Advisory
• https://osv.dev/vulnerability/RUSTSEC-2026-0141 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-46428 · Security Note
• https://github.com/lettre/lettre/releases/tag/v0.11.22 · Note
• https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35 · Note
• https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53 · Note
• https://crates.io/crates/lettre · Note
• https://twitter.com/CVEnew/status/2079238909913891194 · Twitter Post
• https://rustsec.org/advisories/RUSTSEC-2026-0141.html · Note