Vulnerabilities in pkg:gem/mail

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mvxr-6m87-mv2q",
  "modified" : "2026-09-02T22:02:32Z",
  "published" : "2026-09-02T22:02:32Z",
  "aliases" : [ "CVE-2026-63435" ],
  "summary" : "Mail: Email address spoofing via malformed RFC 2047 encoded-words",
  "details" : "## Summary\n\nMail::Utilities.q_value_decode and Mail::Utilities.b_value_decode decoded only the first RFC 2047 encoded-word in a string and used an overly greedy pattern to match the charset token. A crafted, malformed encoded-word embedded in an address display name or local part could cause the decoded output to differ from what a human reviewer or downstream parser would expect, allowing an attacker to spoof the apparent sender/recipient address.\n\n## Details\n\nBoth decoders used a single String#match against a pattern such as /\\=\\?(.+)?\\?[Qq]\\?(.*)\\?\\=/m. Two problems:\n\n1. Single match, dropped remainder. Only the first =?charset?Q?...?= (or ?B?) word was decoded. Any additional encoded-words or surrounding text were not handled consistently, so the decoded result could silently omit or alter parts of the input.\n2. Greedy charset capture. (.+)? is greedy and matches across ? delimiters, so a malformed word could span more of the string than a strict RFC 2047 parse would, changing the boundary between \"encoded\" and \"literal\" text.\n\n## Impact\n\nApplications using mail to parse and display or authorize based on decoded header values (From, To, Reply-To, etc.) may present or act on an address different from the one a validator inspecting the raw header would see. Primary risk is spoofing / phishing and authorization-check bypass. No RCE.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "mail"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.9.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-63435"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mikel/mail/pull/1664"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mikel/mail"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mikel/mail/releases/tag/2.9.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-436" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-02T22:02:32Z",
    "nvd_published_at" : "2026-09-01T21:18:35Z"
  }
}