CVE-2026-45300

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. Versions on the 2.x branch prior to 2.15.0 and the 3.x branch prior to 3.0.10 leak Cookie headers to cross-origin redirect targets. When following a redirect to a different origin, the propagatedHeaders() method in Redirect30xInterceptor.java strips Authorization and Proxy-Authorization headers but does not strip the Cookie header, causing session cookies and other sensitive cookie values to be sent to attacker-controlled servers. Versions 2.15.0 and 3.0.10 patch the issue.

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. Versions on the 2.x branch prior to 2.15.0 and the 3.x branch prior to 3.0.10 leak Cookie headers to cross-origin redirect targets. When following a redirect to a different origin, the propagatedHeaders() method in Redirect30xInterceptor.java strips Authorization and Proxy-Authorization headers but does not strip the Cookie header, causing session cookies and other sensitive cookie values to be sent to attacker-controlled servers. Versions 2.15.0 and 3.0.10 patch the issue.

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:

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:

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

    if (!keepBody) {
        headers.remove(CONTENT_TYPE);
    }

    if (stripAuthorization || (realm != null && (realm.getScheme() == AuthScheme.NTLM
            || realm.getScheme() == AuthScheme.SCRAM_SHA_256))) {
        headers.remove(AUTHORIZATION)
                .remove(PROXY_AUTHORIZATION);
        // BUG: COOKIE is not removed here, so cookies leak across the security boundary.
    }
    return headers;
}

The companion test class RedirectCredentialSecurityTest covers Authorization / Proxy-Authorization stripping on cross-origin redirects and scheme downgrades, but has no coverage for Cookie, which is why the regression went unnoticed.

Proof of concept

import org.asynchttpclient.*;

AsyncHttpClient client = asyncHttpClient();

// trusted-api.com responds 302 -> https://evil.com
Request request = new RequestBuilder("GET")
        .setUrl("https://trusted-api.com/endpoint")
        .setHeader("Cookie", "session=abc123; csrf=xyz789; api_key=secret")
        .setHeader("Authorization", "Bearer token123")
        .build();

client.executeRequest(request).get();

// Request seen by evil.com after the redirect:
//   Authorization: <stripped>
//   Cookie:        session=abc123; csrf=xyz789; api_key=secret   <-- leaked

Impact

• Session hijacking — leaked session cookies allow impersonation.
• CSRF token theft — CSRF tokens carried in cookies are disclosed.
• API key theft — API keys stored in cookies are disclosed.
• Privacy — tracking identifiers leak to third-party origins.

Realistic attack paths:

• Open-redirect in a trusted API endpoint.
• Compromised CDN or API gateway injecting redirects.
• MITM on a plaintext hop in the redirect chain.

Fix

Add COOKIE to the headers removed alongside AUTHORIZATION / PROXY_AUTHORIZATION on the security-boundary branch:

if (stripAuthorization) {
    headers.remove(AUTHORIZATION)
            .remove(PROXY_AUTHORIZATION)
            .remove(COOKIE);
} else if (realm != null && (realm.getScheme() == AuthScheme.NTLM
        || realm.getScheme() == AuthScheme.SCRAM_SHA_256)) {
    headers.remove(AUTHORIZATION)
            .remove(PROXY_AUTHORIZATION);
}

Note that the URI-scoped CookieStore will re-add any cookies that legitimately match the new target after propagatedHeaders returns, so legitimate cross-origin sessions tracked by the client are not broken.

Fixed in 3.0.10 and 2.15.0 by commit…

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. Versions on the 2.x branch prior to 2.15.0 and the 3.x branch prior to 3.0.10 leak Cookie headers to cross-origin redirect targets. When following a redirect to a different origin, the propagatedHeaders() method in Redirect30xInterceptor.java strips Authorization and Proxy-Authorization headers but does not strip the Cookie header, causing session cookies and other sensitive cookie values to be sent to attacker-controlled servers. Versions 2.15.0 and 3.0.10 patch the issue.

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. Versions on the 2.x branch prior to 2.15.0 and the 3.x branch prior to 3.0.10 leak Cookie headers to cross-origin redirect targets. When following a redirect to a different origin, the propagatedHeaders() method in Redirect30xInterceptor.java strips Authorization and Proxy-Authorization headers but does not strip the Cookie header, causing session cookies and other sensitive cookie values to be sent to attacker-controlled servers. Versions 2.15.0 and 3.0.10 patch the issue.

The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. Versions on the 2.x branch prior to 2.15.0 and the 3.x branch prior to 3.0.10 leak Cookie headers to cross-origin redirect targets. When following a redirect to a different origin, the propagatedHeaders() method in Redirect30xInterceptor.java strips Authorization and Proxy-Authorization headers but does not strip the Cookie header, causing session cookies and other sensitive cookie values to be sent to attacker-controlled servers. Versions 2.15.0 and 3.0.10 patch the issue.