MyBB: Contact page reflected XSS

{
  "id": "4eaf96d67dde17c42afb3a130d77aa8bf8364149ce4ea89577685df587bd5eb4",
  "url": "https://osv.dev/vulnerability/CVE-2026-45118",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "MyBB: Contact page reflected XSS",
    "summary": "MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirect target from the from HTTP parameter in $mybb->input['from'] or the Referer HTTP header in $_SERVER['HTTP_REFERER'] and passes it to redirect() without sufficient verification. A javascript: URI becomes the target of the `Click here if you don't want to wait any longer` link because $force_redirect is true, allowing script execution when a victim selects the link. This issue is fixed in version 1.8.40.",
    "evidence": "osv:CVE-2026-45118",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-45118",
      "aliases": [
        "CVE-2026-45118",
        "GHSA-wf92-5q5h-qr53"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/mybb/mybb",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "e9942c6d19ac1709b3df7357cfb8810774c8d3ac"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "fixed": "e9942c6d19ac1709b3df7357cfb8810774c8d3ac"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "mybb_1840"
                  }
                ]
              }
            }
          ],
          "versions": [
            "mybb_1839",
            "mybb_1839_build",
            "mybb_1838",
            "mybb_1838_build",
            "mybb_1837",
            "mybb_1837_build",
            "mybb_1836",
            "mybb_1835_build",
            "mybb_1835",
            "mybb_1834",
            "mybb_1834_build",
            "mybb_1833",
            "mybb_1833_build",
            "mybb_1832",
            "mybb_1832_build",
            "mybb_1831",
            "mybb_1831_build",
            "mybb_1829",
            "mybb_1828",
            "mybb_1828_build",
            "mybb_1827_build",
            "mybb_1827",
            "mybb_1823_build",
            "mybb_1823",
            "mybb_1822",
            "mybb_1822_build",
            "mybb_1821pl1",
            "mybb_1821",
            "mybb_1821_build",
            "mybb_1817_build",
            "mybb_1817",
            "mybb_1820",
            "mybb_1820_build",
            "mybb_1820-rc",
            "mybb_1819",
            "mybb_1818",
            "mybb_1819_build",
            "mybb_1818_build",
            "mybb_1816",
            "mybb_1816_build",
            "mybb_1815",
            "mybb_1815_build",
            "mybb_1814",
            "mybb_1813",
            "mybb_1812",
            "mybb_1811",
            "mybb_1810",
            "mybb_1809",
            "mybb_1808",
            "mybb_1807",
            "mybb_1806",
            "mybb_1805",
            "mybb_1804",
            "mybb_1800",
            "mybb_1801"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45118.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:26.989774670Z",
      "provider": "osv",
      "references": [
        "https://github.com/mybb/mybb/releases/tag/mybb_1840",
        "https://mybb.com/versions/1.8.40",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45118.json",
        "https://github.com/mybb/mybb/security/advisories/GHSA-wf92-5q5h-qr53",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-45118"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-83"
        ],
        "cna_assigner": "GitHub_M",
        "unresolved_ranges": [
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "fixed": "1.8.40"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StringRangeExpression"
              }
            ]
          },
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "fixed": "1.8.40"
                  },
                  {
                    "fixed": "1.8.40"
                  }
                ],
                "source": "DESCRIPTION"
              }
            ]
          }
        ],
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45118.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-45118",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 493375,
  "published_at": "2026-08-18T15:55:27.28+00:00"
}