← Vulnerability feed

Vulnerability record · CVE-2026-46428 · published 20 July 2026

CVE-2026-46428: Improper certificate validation vulnerability

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.

9.1 CVSS 4.0 Critical EPSS 0.32% · top 77.6% CWE-295 · Improper certificate validation Deferred
9.1CVSS 4.0 base score
0.32%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
5References
23 Jul 2026Last modified by NVD

Description

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:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35
https://github.com/lettre/lettre/releases/tag/v0.11.22
https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53
https://rustsec.org/advisories/RUSTSEC-2026-0141.html
https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53

Track CVE-2026-46428 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2026-85102Checkpoint gaia embedded improper certificate validation vulnerabilityImproper certificate trust validation during VPN negotiation in Check Point Quantum Security Gateway may allow an unauthenticated remote attacker to …KEVEPSS 0.99%5.5CVE-2023-41991Apple iOS, iPadOS and macOS certificate validation bypassApple iOS, iPadOS and macOS contain an improper certificate validation flaw (CWE-295) that lets a malicious app bypass signature validation. Apple st…KEVEPSS 13%analysed7.8CVE-2023-20963Android WorkSource parcel mismatch local privilege escalationCVE-2023-20963 is a parcel mismatch in Android's WorkSource component that allows a local attacker to escalate privileges without additional executio…KEVEPSS 1.5%analysed8.8CVE-2022-26923Microsoft Active Directory Domain Services certificate validation privilege escalationActive Directory Domain Services fails to properly validate certificate attributes, allowing a low-privileged domain user to obtain a certificate tha…KEVEPSS 84%analysed8.0CVE-2022-20703Cisco Small Business RV Series Routers stack-based buffer overflowCVE-2022-20703 covers multiple vulnerabilities in Cisco Small Business RV160, RV260, RV340 and RV345 Series Routers, including a stack-based buffer o…KEVEPSS 9.2%analysed8.1CVE-2020-0601Windows CryptoAPI ECC certificate validation spoofing flawWindows CryptoAPI (Crypt32.dll) improperly validates Elliptic Curve Cryptography certificates, allowing a spoofed code-signing certificate to be trus…KEVEPSS 89%analysed

Source: NIST National Vulnerability Database (record CVE-2026-46428), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.