CVE-2026-104890: Kunstmaan CMS Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-p279-5wcv-45vq",
  "modified" : "2026-10-07T18:05:38Z",
  "published" : "2026-10-07T18:05:38Z",
  "aliases" : [ "CVE-2026-104890" ],
  "summary" : "Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution",
  "details" : "### Summary\n\nThe MediaBundle blocks dangerous upload extensions with a blacklist that was matched\ncase-sensitively, while the stored filename was lowercased afterwards. A file uploaded\nas `webshell.pHp` therefore bypassed the blacklist and was written to the web-accessible\nupload directory as `webshell.php`, where the web server executed it. Any authenticated\nbackend user with access to the media section could obtain remote code execution.\n\n### Details\n\n`FileHandler::getFilePath()` rewrote blacklisted extensions to `.txt` using a\ncase-sensitive regex, and only then lowercased the extension when building the stored\nname — so the check ran against the attacker-controlled casing and the normalisation\nhappened after it.\n\nTwo further weaknesses contributed:\n\n* The default blacklist contained only `php` and `htaccess`, leaving other\n  server-executable extensions (`phtml`, `php5`, `phar`, `shtml`, `cgi`, …) unblocked\n  regardless of casing.\n* Configured blacklist values were interpolated into the regex unescaped.\n\n### Impact\n\nAn authenticated user with access to the admin media section can upload a file that the\nweb server executes as PHP. The uploaded file is reachable over HTTP without\nauthentication, giving arbitrary code execution as the web server user.\n\n### Patches\n\nFixed in kunstmaan/media-bundle 7.3.2. The extension is now normalised before it is\nchecked and compared with `in_array()`; the default blacklist is expanded to the full\nset of server-executable extensions; and a new opt-in `allowed_extensions` option allows\nprojects to enforce a strict allow-list.\n\nNote that the patch does not rename files already stored on disk. Sites should audit\ntheir media upload directory for existing files with an executable extension.\n\n### Workarounds\n\nIf you cannot upgrade, configure the web server to refuse to execute scripts in the\nmedia upload directory (for example a `location` block in nginx or `php_flag engine off`\nin Apache).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "kunstmaan/media-bundle"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.3.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "kunstmaan/bundles-cms"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.3.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Kunstmaan/KunstmaanBundlesCMS/security/advisories/GHSA-p279-5wcv-45vq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-104890"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Kunstmaan/KunstmaanBundlesCMS/commit/1bbdfdeac8e7e91506b1a9271360b9b68d7690d3"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Kunstmaan/KunstmaanBundlesCMS"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Kunstmaan/KunstmaanBundlesCMS/releases/tag/7.3.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-434" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-07T18:05:38Z",
    "nvd_published_at" : "2026-10-05T16:17:06Z"
  }
}