rustsec-2026-0141
Vulnerability from osv_rustsec
Published
2026-05-14 12:00
Modified
2026-05-14 09:14
Summary
TLS hostname verification disabled when using Boring TLS backend
Details

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).

Severity
9.1 (Critical)
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
References
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "categories": [
          "crypto-failure"
        ],
        "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",
        "informational": null
      },
      "ecosystem_specific": {
        "affected_functions": null,
        "affects": {
          "arch": [],
          "functions": [],
          "os": []
        }
      },
      "package": {
        "ecosystem": "crates.io",
        "name": "lettre",
        "purl": "pkg:cargo/lettre"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.10.1"
            },
            {
              "fixed": "0.11.22"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "versions": []
    }
  ],
  "aliases": [
    "GHSA-4pj9-g833-qx53"
  ],
  "database_specific": {
    "license": "CC0-1.0"
  },
  "details": "An inverted-boolean bug in lettre\u0027s `boring-tls` integration silently\ndisables TLS hostname verification for callers using the default (strict)\nconfiguration. An on-path attacker presenting any chain-valid certificate\nfor any domain can intercept SMTP submission, including PLAIN/LOGIN\ncredentials and message contents, against any lettre user built with the\n`boring-tls` feature. Other TLS backends (`native-tls`, `rustls`) are\nunaffected.\n\nThe bug was introduced in v0.10.1 and persists through v0.11.21 (latest).",
  "id": "RUSTSEC-2026-0141",
  "modified": "2026-05-14T09:14:38Z",
  "published": "2026-05-14T12:00:00Z",
  "references": [
    {
      "type": "PACKAGE",
      "url": "https://crates.io/crates/lettre"
    },
    {
      "type": "ADVISORY",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0141.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/lettre/lettre/security/advisories/GHSA-4pj9-g833-qx53"
    }
  ],
  "related": [],
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "TLS hostname verification disabled when using Boring TLS backend"
}


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