Mail: Email address spoofing via malformed RFC 2047 encoded-words

{
  "id": "b051290d210e65dcd716282a5e0f51de02c0df20e708ff4a6c5d2ad0a83bddc9",
  "url": "https://osv.dev/vulnerability/CVE-2026-63435",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Mail: Email address spoofing via malformed RFC 2047 encoded-words",
    "summary": "Mail is an internet library for Ruby designed to handle email generation, parsing, and sending. Prior to 2.9.1, Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode used a single String#match and an overly greedy charset capture to decode only the first RFC 2047 encoded-word and mishandle surrounding or subsequent text. A crafted malformed encoded-word in an address display name or local part could cross ? delimiters and make decoded From, To, or Reply-To header values differ from the raw values inspected by a human reviewer or downstream parser, enabling apparent sender or recipient spoofing, phishing, or authorization-check bypass. This issue is fixed in version 2.9.1.",
    "evidence": "osv:CVE-2026-63435",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-63435",
      "aliases": [
        "CVE-2026-63435",
        "GHSA-mvxr-6m87-mv2q"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mikel/mail",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "d645d7b5b7d03218b0bc8971ef041c991a63f5f7"
                },
                {
                  "fixed": "f9d59c2e447af42e2c3dec5a56b1bb25c7292859"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.9.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "f9d59c2e447af42e2c3dec5a56b1bb25c7292859"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "d645d7b5b7d03218b0bc8971ef041c991a63f5f7"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "2.9.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.7.0",
            "2.7.0.rc3",
            "2.7.0.rc2",
            "2.7.0.rc1",
            "2.6.4",
            "2.6.3",
            "2.6.1",
            "2.6.0",
            "2.4.4",
            "2.5.3",
            "2.5.2",
            "2.5.1",
            "2.5.0",
            "2.4.3",
            "2.4.2",
            "2.3.0",
            "2.4.1",
            "2.2.18",
            "2.2.17",
            "2.2.15",
            "2.2.14",
            "2.2.13",
            "2.2.11",
            "2.2.10",
            "2.2.9",
            "2.2.8",
            "2.2.6",
            "2.2.5.2",
            "2.2.5.1",
            "2.2.5",
            "2.2.4",
            "2.2.3",
            "2.2.2",
            "2.2.0",
            "2.1.3",
            "2.1.2",
            "2.0.5",
            "2.0.3"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63435.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.321039813Z",
      "provider": "osv",
      "references": [
        "https://github.com/mikel/mail/releases/tag/2.9.1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63435.json",
        "https://github.com/mikel/mail/security/advisories/GHSA-mvxr-6m87-mv2q",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-63435",
        "https://github.com/mikel/mail/commit/f9d59c2e447af42e2c3dec5a56b1bb25c7292859",
        "https://github.com/mikel/mail/pull/1664"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-436"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63435.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-63435",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 522218,
  "published_at": "2026-09-01T20:09:20.82+00:00"
}