Affected: Maven: org.asynchttpclient:async-http-client

## Summary

async-http-client leaks `Cookie` headers to cross-origin redirect targets. When following a redirect across a security boundary (different origin, or HTTPS→HTTP downgrade), the `propagatedHeaders()` method in `Redirect30xInterceptor.java` strips `Authorization` and `Proxy-Authorization` headers but does not strip `Cookie`, so session cookies and other sensitive cookie values are forwarded to the redirect target — which may be attacker-controlled.

## Details

The vulnerability is in `client/src/main/java/org/asynchttpclient/netty/handler/intercept/Redirect30xInterceptor.java`.

The caller computes `stripAuth` on each redirect:

```java boolean sameBase = request.getUri().isSameBase(newUri); boolean stripAuth = !sameBase || schemeDowngrade || stripAuthorizationOnRedirect; // ... requestBuilder.setHeaders(propagatedHeaders(request, realm, keepBody, stripAuth)); ```

`stripAuth` is `true` whenever the redirect crosses an origin, downgrades the scheme, or the caller opted in via `AsyncHttpClientConfig#isStripAuthorizationOnRedirect()`.

In the vulnerable version, `propagatedHeaders()` only removes `Authorization` and `Proxy-Authorization` in that branch — `Cookie` is left untouched:

```java private static HttpHeaders propagatedHeaders(Request request, Realm realm, boolean keepBody, boolean stripAuthorization) { HttpHeaders headers = request.getHeaders() .remove(HOST) .remove(CONTENT_LENGTH);

if (!keepBody) { headers.remo…