TLS hostname verification disabled when using Boring TLS backend

{
  "id": "d9b0d309696597f3f5602f67b61954bead40394db556534dbd79e87dd881fc1b",
  "url": "https://osv.dev/vulnerability/RUSTSEC-2026-0141",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "TLS hostname verification disabled when using Boring TLS backend",
    "summary": "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).",
    "evidence": "osv:RUSTSEC-2026-0141",
    "products": [
      {
        "name": {
          "value": "lettre",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "0.11.22",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "RUSTSEC-2026-0141",
      "aliases": [
        "CVE-2026-46428",
        "GHSA-4pj9-g833-qx53",
        "RUSTSEC-2026-0141"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.10.1"
                },
                {
                  "fixed": "0.11.22"
                }
              ]
            }
          ],
          "package": {
            "name": "lettre",
            "purl": "pkg:cargo/lettre",
            "ecosystem": "crates.io"
          },
          "database_specific": {
            "cvss": "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",
            "source": "https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0141.json",
            "categories": [
              "crypto-failure"
            ],
            "informational": null
          },
          "ecosystem_specific": {
            "affects": {
              "os": [],
              "arch": [],
              "functions": []
            },
            "affected_functions": null
          }
        }
      ],
      "modified": "2026-10-12T18:00:14.045169536Z",
      "provider": "osv",
      "references": [
        "https://crates.io/crates/lettre",
        "https://rustsec.org/advisories/RUSTSEC-2026-0141.html",
        "https://github.com/lettre/lettre/commit/f5efffc88360dbdbfcef80f465e42d5bce68ca35"
      ],
      "provider_metadata": {
        "license": "CC0-1.0"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-46428",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 306452,
  "published_at": "2026-05-14T12:00:00+00:00"
}