CVE-2026-55778: parse-server Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v8x7-r927-cc93",
  "modified" : "2026-06-19T19:36:36Z",
  "published" : "2026-06-19T19:36:36Z",
  "aliases" : [ "CVE-2026-55778" ],
  "summary" : "parse-server: Stored XSS via non-standard file extension bypassing file upload extension blocklist",
  "details" : "### Impact\n\nParse Server's default `fileUpload.fileExtensions` blocklist is intended to prevent uploading files that browsers render as active content (such as HTML and SVG), which can be used to perform stored cross-site scripting (XSS) attacks against other users. The blocklist could be bypassed by uploading a file whose extension is not an exact match of a blocked extension (for example a non-standard or compound extension) together with a dangerous content type. On storage adapters that persist and serve the uploaded content type (such as S3 and GCS), the file is then served with the attacker-supplied content type, enabling stored XSS against users who open the file URL.\n\nThis affects the default configuration, in which authenticated users are allowed to upload files. The default GridFS/filesystem adapter sets the `X-Content-Type-Options: nosniff` response header, which mitigates browser rendering on that adapter, but the upload restriction itself is still bypassed. This is an incomplete-fix follow-up of GHSA-vr5f-2r24-w5hc and GHSA-7wqv-xjf3-x35v.\n\n### Patches\n\nThe file upload extension validation now also evaluates the request content type against the configured blocklist whenever the filename's extension is not a recognized type. As a result, a dangerous content type can no longer be preserved by uploading a file with a non-standard extension, and such uploads are rejected.\n\n### Workarounds\n\nConfigure `fileUpload.fileExtensions` as a strict allowlist of only the file extensions your application needs (for example `[\"^(png|jpe?g|gif|pdf)$\"]`) instead of relying on the default blocklist. Additionally, serve uploaded files from a separate domain than the application, so that any executed content is isolated from the application's origin.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "parse-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "9.0.0"
      }, {
        "fixed" : "9.9.1-alpha.11"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "parse-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.6.81"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 8.6.80"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/parse-community/parse-server/security/advisories/GHSA-v8x7-r927-cc93"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/parse-community/parse-server/pull/10505"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/parse-community/parse-server/pull/10506"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/parse-community/parse-server"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-434" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T19:36:36Z",
    "nvd_published_at" : null
  }
}